Mollusks, arthropods, crustaceans and arachnids. Biology at the Lyceum What is the basis for the complex behavior of spiders to build

The complex behavior of spiders - their "industry", that is, the construction of trapping nets, flight devices, underground or underwater dwellings, as well as the "care for offspring" developed in many species - may seem like a manifestation of intelligent activity of the same order as conscious human activity.

However, a study of the way of life of spiders clearly shows that the basis of their psychological activity is more or less complex instincts, that is, characteristic of everyone. separate species certain norms of behavior that are not acquired by personal experience, but constitute a specific feature of a given animal.

Like all other species characteristics - a certain form of the body, the location of the eyes, the pattern on the surface of the abdomen, etc. - the instincts are inherited from generation to generation and immediately, already in finished form, appear at the appropriate age or at the appropriate stage of development.

So, for example, newborn cubs of the cross, leaving the egg cocoon only the next spring, that is, a few months after the death of their parents, stay in this cocoon all together, but in case of danger they scatter in different directions - “crumble like beads”.

Their behavior turns out to be very expedient: if, as the proverb says, it is impossible to immediately chase two hares, then it is even more difficult to chase a hundred spiderlings scattering in all directions at a time. But now the danger has passed, and the tiny spiderlings again gather under the shelter of a silky cocoon arranged by their mother, which protects them well from rain and dew.

The cubs of wandering spiders - tarantulas and smaller forms of eight-legged "wolves" behave quite differently. In these species, females "caringly" carry their egg cocoon with them, and when the eggs hatch, they begin to crawl over the mother's body or roam leisurely around her.

However, at the slightest alarm, spiderlings instantly gather in a tight heap on the mother's torso, which can really protect them from attacks.

But the days go by, and the close "friendship" between the brothers and sisters disappears: the grown predators scatter apart and, when they meet, treat each other as if they were a possible prey. This new instinct also turns out to be very useful, since it can be difficult for several predators to feed in one place and each of them occupies a separate hunting area for itself.

Young cobweb spiders begin to weave a snare, and at the same time it turns out that they, who have never seen how their parents did, immediately "know how" to build them, and moreover, in exactly the way that is typical this species spiders: crosses - in the form of a vertically stretched network, spiders of the genus Linifia - in the form of a horizontal arch. No one teaches a silver spider to build his underwater bell and carry air into it and so on.

We should not be surprised that these hereditary norms of behavior turn out to be well suited to the animal's life situation: as a result of the constant action of selection, animals that do not satisfy the "requirements" of the environment in terms of their bodily characteristics or according to their inherent instincts are inevitably subject to destruction.

Even such seemingly bizarre poses and “dances” that precede mating in spiders are explained by the fact that spiders are devoid of smell and can only see clearly at close range: therefore, visual signals remain almost the only way for them to to be seen by individuals of the opposite sex and not be mistaken for approaching prey.

Those spiders in which the hereditary instinct of “marriage games” or “dances” would not have manifested at the appropriate moment would either remain unfertilized or would be eaten, like an insect carelessly approaching, that is, in both cases they would be left without offspring.

Therefore, despite the outward similarity of the behavior of spiders with manifestations of intelligent activity, we have no right to "humanize" their actions or attach any moral assessment to them. It should not seem to us an incomprehensible contradiction of the behavior of the female tarantula, which after mating often “cannibalistically” eats the male who did not have time to escape, and then turns out to be an extremely “tender” mother, “caringly” dragging her egg cocoon with her everywhere, and after hatching, the spiders are just as “ carefully” guarding her numerous offspring.

The fact is that in spiders, the life of a male after he has performed his sexual function is no longer of value for the preservation of the species, and in females, after mating, their usual instinct towards crawling prey comes into force. As for maternal “concerns for offspring”, if the female did not manifest the corresponding instinct at the appropriate time in her life, her small, weak and defenseless offspring would be doomed to death, and, consequently, any deviation from this useful (in the data conditions!) for species life, the norms of behavior are invariably swept away by the action of natural selection.

Class Arachnida (Arachnida)

Arachnids are terrestrial chelicerates with a large cephalothorax bearing short claw-shaped or claw-shaped chelicerae, long pedipalps, and four pairs of long walking legs. The abdomen is devoid of limbs. Breathe through lungs or trachea. In addition to the coxal glands characteristic of aquatic forms, they have Malpighian vessels.

For many arachnids, the secretion of arachnoid threads from special spider glands. The web plays a significant role in the life of arachnids: in the extraction of food, protection from enemies, resettlement of juveniles, etc.

The Latin name of arachnids Arachnida is given by the name of the heroine of myths Ancient Greece- the needlewoman Arachne, turned by Athena into a spider.

External structure. Arachnids are extremely diverse in body shape and size, segmentation, and limb structure. They differ from primary aquatic chelicerae in adaptations to life on land. They have thinner chitinous covers, which lightens the weight of their body, which is important for land animals. In addition, as part of the chitinous cuticle, they have a special outer layer - the epicuticle, which protects the body from drying out. In arachnids, the gill legs on the abdomen have disappeared, and instead, air-respiratory organs, lungs or tracheas, have appeared. The rudiments of the abdominal legs in them perform sexual, respiratory functions or have turned into arachnoid warts. The walking legs of arachnids are longer than those of aquatic chelicerae and are adapted for movement on land.

Within the class of arachnids, oligomerization of body segmentation is observed until the complete fusion of all segments. There are several types of body dissection in arachnids, the most important of which are as follows.

The scorpions, similar in external morphology to fossil crustacean scorpions, are characterized by the greatest dissection of the body (Fig. 295). The cephalothorax of scorpions, like most chelicerae,

fused and consists of an acron and seven segments, of which the last segment is reduced. The abdomen is subdivided into the anterior abdomen of six wide segments and the posterior abdomen of six narrow segments and a telson with a poisonous needle.

Solputas have a more primitive division of the cephalothorax than other arachnids: the acron and the first four segments are fused, while the last three segments are free, of which the very last segment is rudimentary. A similar dismemberment is observed in some ticks.

The harvestmen have a fused cephalothorax, and the abdomen consists of nine segments and a telson, which is fused with the last abdominal segment. The abdominal region is no longer subdivided into the anterior and posterior abdomen. A similar dismemberment is also characteristic of haymaking mites.

Rice. 295. Scorpion Buthus eupeus: A - view from the dorsal side and B - from the ventral side (according to Byalynitsky-Birula); VIII-XIX - abdominal segments; 1 - cephalothorax, 2 - chelicerae, 3 - pedipalp, 4 - leg, 5 - telson, 6 - poisonous needle, 7 - posterior abdomen, 8 - anterior abdomen, 9 - anus, 10 - pulmonary fissures, 11 - comb organs, 12 - sex caps

Spiders have a fused cephalothorax and abdomen. Due to the seventh segment of the cephalothorax, a constriction is formed between the cephalothorax and abdomen. The abdomen is formed by 11 fused segments and a telson.

The body of most ticks is completely fused.

The limbs of arachnids are diverse in form and function. Chelicerae are functionally similar to crayfish mandibles. These organs serve to crush food or bite through the victim. They can be claw-like, like in scorpions, salpug, or claw-like, like in spiders, or stiletto-like, like in many ticks. Pedipalps may serve to capture or hold prey. Grasping pedipalps with a claw at the end are characteristic of scorpions and false scorpions. Salpug pedipalps are flagellate and perform a sensory function. In spiders, pedipalps are similar to the mouth tentacles of insects. Tactile, olfactory sensilla are concentrated on them. In males of many spiders, copulatory organs are located on the pedipalps. In some ticks, pedipalps, together with chelicerae, are part of the piercing-sucking mouthparts. The four pairs of walking legs in all arachnids consist of 6-7 segments and are used for locomotion. In solpugs, telifons, the first pair of walking legs performs the function of sensory organs. There are many tactile hairs on the legs of arachnids, which compensates for their lack of antennae characteristic of other arthropods.

On the abdominal region of some arachnids there are rudiments of limbs that perform various functions. So, in scorpions, on the first segment of the abdomen, there are paired genital opercula covering the genital openings, on the second, special sensory comb-like organs, and on segments 3-6 m, lungs - modified gill legs. Spiders on the underside of the abdomen have 1-2 pairs of lungs and 2-3 pairs of appendages - arachnoid warts, which are modified rudiments of limbs. Some lower ticks have three pairs of coxal organs on their abdomens, which are appendages of coxae (coxae) of reduced legs.

The integument is represented by skin - the hypodermis, which secretes a chitinous cuticle, consisting of two or three layers. The epicuticle is well developed in spiders and harvestmen, as well as in some mites. The cuticle of many arachnids glows in the dark, due to the special structure of chitin, which polarizes transmitted light. Skin derivatives include poisonous glands at the base of chelicerae in spiders and a poisonous needle in scorpions, spider glands of spiders, pseudoscorpions, and some mites.

Internal structure. The digestive system of arachnids consists of three sections (Fig. 296). Depending on the type of food, the structure

intestine varies. A particularly complex structure of the digestive system is observed in predatory arachnids with extraintestinal digestion. This way of feeding is especially characteristic of spiders. They pierce the victim with chelicerae, inject poison and digestive juices of the salivary glands and liver into the victim. Under the influence of proteolytic enzymes, the tissues of the victim are digested. Then the spider sucks in half-digested food, and only covers remain from the victim. On the web of a spider, you can often see the covers of insects sucked out by it.

In the structure of the intestines of spiders, there are a number of adaptations to this method of nutrition. The foregut, lined with a cuticle, consists of a muscular pharynx, esophagus, and sucking stomach. Due to the contraction of the muscles of the pharynx and especially the stomach, the spider absorbs liquid semi-digested food. The middle intestine in the cephalothorax forms blind processes (in spiders - five pairs). This allows spiders and other arachnids to ingest large volumes of liquid food. The middle intestine in the abdominal region forms paired glandular protrusions - the liver. The liver functions not only as a digestive gland, phagocytosis occurs in it - intracellular digestion. Spiders have four pairs of liver appendages. The posterior part of the midgut forms a swelling into which the excretory tubules of the Malpighian vessels empty. Excrements and excretions are formed here, which are then excreted through the short hindgut to the outside. Arachnids can starve for a long time, as they have reserves nutrients in a special spare tissue - the fatty body located in the mixocele.

Rice. 296. Scheme internal structure spider (neg. Aranei) (from Averintsev): 1 - eyes, 2 - poisonous gland, 3 - chelicera, 4 - brain, 5 - mouth, 6 - subesophageal ganglion, 7 - outgrowths of the middle intestine, 8 - base of walking legs, 9 - lung, 10 - spiracle, 11 - oviduct, 12 - ovary, 13 - arachnoid glands, 14 - arachnoid warts, 15 - anus, 16 - Malpighian vessels, 17 - ostia, 18 - liver ducts, 79 - heart, 20 - pharynx

excretory system. The excretory organs are represented by coxal glands and malpighian vessels. There are 1-2 pairs of coxal glands in the cephalothorax, which correspond to the coelomoducts. The glands consist of a mesodermal glandular sac, from which a convoluted canal departs, passing into a direct excretory canal. The excretory openings open at the base of the coxae of the third or fifth pairs of limbs. Coxa, or coxa, is the basal segment of the legs of arthropods. The position of the excretory glands near cox walking legs was the basis for their name - coxal. In embryogenesis, the coxal glands are laid down in all arachnids, but in adult animals they are often underdeveloped.

Malpighian vessels are special excretory organs characteristic of land arthropods. In arachnids, they are of endodermal origin and open into the posterior midgut. Malpighian vessels secrete excretions - grains of guanine. In the intestines, moisture is drawn from the excreta, which saves water loss in the body.

Respiratory system. Arachnids developed two types of respiratory organs: lungs and tracheas. There is a hypothesis that the lungs of arachnids were formed from the abdominal gill legs of crustaceans. This is evidenced by their lamellar structure. So, in scorpions, the lungs are located on 3-6 m segments of the abdomen and are deep protrusions, in which there are thin pinnate leaves from the inside. In their structure, the lungs of arachnids are similar to the gill legs of aquatic chelicerae, immersed in skin cavities (Fig. 297). Lungs are also found in flagellates (two pairs) and spiders (1-2 pairs).

The trachea are also the organs of air respiration in land chelicerae. They are skin invaginations in the form of thin tubules. Probably, tracheae arose independently in different phylogenetic lineages of arachnids. This is evidenced by the different arrangement of stigmas (breathing holes) in different arachnids: in most - on the 1st-2nd segments of the abdomen, in salpugs - on the 2nd-3rd segments of the abdomen and on the cephalothorax and an unpaired stigma on the fourth segment of the abdomen, in two-lungs spiders - on the last segments of the abdomen, and in some - at the base of chelicerae or walking legs or at the site of reduced lungs. The most powerfully developed tracheal system in salpugs, in which longitudinal trunks and branches are distinguished, passing into different parts of the body (Fig. 298).

Different orders of arachnids have different respiratory organs. Only pulmonary respiration is characteristic of scorpions, flagellated and four-lung spiders. Tracheal breathing is characteristic of most arachnids: pseudoscorpions, salpugs, haymakers, ticks and some

spiders. Bi-lung spiders have one pair of lungs and one pair of windpipes. Some small ticks do not have respiratory organs and breathe through the skin.

Circulatory system open. The heart is on the dorsal side of the abdominal region. In arachnids with a pronounced dismemberment of the body, the heart is long, tubular with a large number of awns; for example, scorpions have seven pairs of ostia, while in other arachnids the heart shortens and the number of ostia decreases. So, spiders have a heart with 3-4 pairs of ostia, and ticks have one pair. Some small ticks have a reduced heart.

Nervous system. The brain consists of two sections: the protocerebrum, which innervates the eyes, and the tritocerebrum, which innervates the chelicerae (Fig. 299). The deutocerebrum, characteristic of other arthropods that have the first pair of antennae, is absent in arachnids.

The ventral nerve cord innervates the remaining limbs of the cephalothorax and abdomen. In arachnids, there is a tendency for the ganglia of the ventral nerve cord to fuse (oligomerization). The most dissected forms, like scorpions, have one fused cephalothoracic ganglion and seven ganglia in the abdominal region. In salpugs, in addition to the cephalothoracic ganglion, there is only one abdominal node; in spiders, only the cephalothoracic ganglion is preserved, while in ticks and harvestmen, only the peripharyngeal ganglionic accumulation is expressed.

sense organs. The organs of vision are poorly developed and are represented by 1, 3, 4, b pairs of simple ocelli on the cephalothorax. Spiders often have eight eyes arranged in two arcs, while scorpions have one pair of large median ocelli and 2-5 pairs of lateral ones.

The main sense organs in arachnids are not eyes, but tactile hairs and trichobothria, which detect air vibrations. Some arachnids have chemical sense organs - lyre-shaped organs. They are small gaps in the cuticle, at the bottom of which sensory processes of nerve cells fit in a soft membrane.

Most arachnids are predators that hunt in the dark, and therefore the organs of touch, seismic sense (trichobothria), and smell are of particular importance for them.

reproductive system. Spider-like dioecious (Fig. 300). Some show sexual dimorphism. In many spiders, males are slightly smaller than females, and they have swellings on their pedipalps - seminal capsules, which they fill with sperm during the breeding season.

Gonads paired or fused. The ducts are always paired, but may flow into an unpaired canal, which opens with a genital opening on the first segment of the abdomen. Males of some species have additional glands, while females have seminal receptacles.

Rice. 300. Reproductive system of arachnids (from Lang): male reproductive system (A - scorpion, B - salpuga); female reproductive system (B - scorpion, D - spider); 1 - testis, 2 - vas deferens, 3 - seminal vesicle, 4 - additional glands, 5 - ovary, 6 - oviduct

Reproduction and development. Fertilization in arachnids can be external-internal or internal. In the first case, males leave spermatophores - packages of sperm on the surface of the soil, and females find them and capture them with the genital opening. Males of some species insert spermatophores into the genital opening of females with the help of pedipalps, while others initially collect sperm in seed capsules on pedipalps (Fig. 301), and then squeeze it into the genital tract of females. Some arachnids are characterized by copulation and internal fertilization.

The development is direct. Eggs hatch into juveniles that look like adults. In some species, eggs develop in the genital tract, and live births are observed (scorpions, pseudoscorpions, some ticks). Metamorphosis is often observed in ticks, and their nymph larvae have three pairs of walking legs, and not four, as in adults.

The arachnid class is subdivided into many orders, of which we will consider the most important: the Scorpion detachment (Scorpiones), the Zhgutopodye detachment (Uropygi), the Solpugi detachment (Solifugae), the Pseudoscorpiones detachment, the Haymakers detachment (Opiliones), the Spider detachment (Aranei) and detachments ticks: Acariformes, Parasitiformes, Opiliocarina (representatives of the orders are shown in Figure 302).

Order of Scorpions (Scorpiones). These are the most ancient arachnids. There are paleontological findings that testify to their origin from aquatic crustacean scorpions. Land scorpions have been known since the Carboniferous.

The scorpion order is characterized by the greatest dismemberment of the body. The fused cephalothorax is followed by six segments of the anterior abdomen and six segments of the posterior abdomen (Fig. 295). The telson forms a characteristic swelling with a poisonous needle. Chelicerae are claw-shaped, closing in a horizontal plane. Pedipalps are prehensile with large claws. Walking legs end in a paw with two claws. Scorpions on all segments of the anterior abdomen have derivatives of the limbs: on the first - paired genital caps, on the second - comb-shaped organs, on the 3rd-6th - lungs, opening with four pairs of respiratory openings (stigmas).

Scorpions live in countries with a warm climate. These are nocturnal predators, hunting mainly for insects, which are grabbed by pedipalps and sting with a needle. They are characterized by live birth and care for offspring. For some time, the female carries her offspring on her back, throwing her back with a poisonous needle on her back.

About 600 species of scorpions are known. The most widely distributed in the Crimea, the Caucasus and Central Asia is the motley scorpion (Buthus eupeus). Scorpion stings in most cases are not dangerous to humans.

Detachment Bitelegs, or Telifones (Uropygi). Phones - tropical group arachnids, including only 70 species. These are relatively large arachnids, up to 7.5 cm long. In Russia, only one species of telephons (Telyphonus amurensis) is found in the Ussuri region.

The main morphological characteristic of telephons is that their first pair of walking legs has turned into long sensory appendages, and many of them have a special long caudal filament, divided into small segments (Fig. 302, B). This is a feeling organ. Chelicerae with claw-like segment, pedipalps claw-shaped. The seventh segment of the cephalothorax forms a constriction on the border with the abdomen. Abdomen 10-segmented, not subdivided into anterior metabelly.

Telifons are nocturnal predators and navigate in space mainly due to the organs of touch and seismic sense located on elongated sensory limbs. Hence the name - teliphones, as they hear the approach of a victim or enemy at a great distance by rustling or weak wave vibrations of the air.

The phones breathe with lungs. They have two pairs of lungs located on the 8th-9th segments. Fertilization is spermatophoric. They lay eggs. The female takes care of the young, carrying them on her back. They have protective anal glands. When threatened, they spray a caustic liquid from the anal glands.

Order Solpuga (Solifugae). Salpugs, or phalanxes, are a detachment of large arachnids that live in steppes and deserts. In total, about 600 species are known. The cephalothorax of the salpug is unfused and consists of a protopeltidia - the head section (acron and 4 segments) and three free segments, of which the last is underdeveloped (Fig. 302, A). The abdomen is 10-segmented. Powerful chelicerae are claw-shaped and close in a vertical plane. Pedipalps are similar to walking legs, they are involved in locomotion and also perform a sensory function. Breathe with trachea. The main tracheal trunks open with paired spiracles on the second and third abdominal segments. In addition, there is an unpaired spiracle on the fourth segment and a pair of additional spiracles on the cephalothorax. Salpugs are not poisonous. They feed mainly on insects. They hunt at night. The most common species is Galeodes araneoides (Crimea, Caucasus) up to 5 cm long. Fertilization is spermatophoric. The eggs are laid in a burrow. The female takes care of the offspring.

Squad Pseudoscorpiones. These are small arachnids (1-7 mm) with large claw-shaped pedipalps and therefore resemble scorpions. Their cephalothorax is fused, and the abdomen is 11-segmented, not divided into anterior and posterior abdomen. The ducts of the spider glands open on the claw-shaped chelicerae. Tracheal stigmas open on the 2nd or 3rd segments of the abdomen.

False scorpions live in the forest floor, under the bark, and also in human dwellings. They are small carnivores that feed on small mites and insects. Fertilization is spermatophoric. The male lays a spermatophore with two horns, and the female crawls onto the spermatophore and inserts its horns into the openings of the seed receptacles. The female lays fertilized eggs in a special brood chamber on the ventral side of the body. The larvae emerging from the eggs are suspended from the bottom of the brood chamber and feed on the yolk secreted from the female's ovaries into her brood chamber.

About 1300 species of false scorpions are known. Book false scorpion (Chelifer cancroides) is not uncommon in houses (Fig. 302, B). Its appearance in book depositories indicates that the mode of storing books has been violated. False scorpions usually appear in damp rooms, where favorable conditions are formed for the development of small insects and ticks - pests of books.

Order Haymakers (Opiliones). This is a large, widespread group of arachnids that look like spiders. Harvestmen differ from spiders in the absence of a constriction between the cephalothorax and abdomen, the articulation of the abdominal region (ten segments) and claw-shaped, rather than hook-shaped, like in spiders, chelicerae. A total of 2500 species are known.

Harvestmen are found everywhere on the surface of the soil, in cracks in the bark of trees, on the walls of houses and fences. They feed on small insects and hunt at night. Breathing is tracheal. There is one pair of stigmas on the first segment of the abdomen on the sides of the genital shield. They are characterized by the ability to autotomy, or self-mutilation. Lost legs are not restored. A predator can only grab a haymaker by the leg, which then breaks off, which saves the haymaker's life. The severed leg of the haymaker twitches convulsively for a long time and resembles a scythe in shape. Therefore, they are often called "spider-hay-mow" or "mow-mow-leg". The legs of the harvesters are climbing, with a multi-segmented tarsus.

Haymakers do not secrete cobwebs and actively hunt for their prey themselves. They play a positive role in reducing the number of insects. On the soil surface and in the grass layer, the density of hayfields often reaches several tens per 1 m2. The most common haymaker (Phalangium opilio, Fig. 302, D), which is found in various natural landscapes and even in cities. The body is brownish, up to 9 mm long, and the legs are up to 54 mm.

Detachment Spiders (Aranei). Spiders are the largest order of arachnids, including more than 27 thousand species. Morphologically, they are well distinguished from other orders. Their body is clearly divided into a fused cephalothorax and a fused rounded abdomen, between which there is

constriction formed by the seventh segment of the cephalothorax. Their chelicerae are hook-shaped, with ducts of poisonous glands. The pedipalps are short, tentacle-shaped. Four pairs of walking legs often end in comb-like claws that serve to stretch the web. On the underside of the abdomen are arachnoid warts. Eyes (usually eight) are located on the cephalothorax. Most spiders (two-lung suborder) have one pair of lungs and a pair of tracheae, and some tropical spiders (four-lung suborder) have only lungs (two pairs).

The web is important in the life of spiders. The complex behavior of spiders due to the use of the web at all stages life cycle determined their wide ecological radiation and flourishing.

From the web, spiders build their dwelling between leaves, branches or in a soil hole. The cobweb envelops the oviposition of spiders with the formation of an egg cocoon. Often, female spiders wear a cocoon under their abdomen, taking care of their offspring. Small spiders secrete a long cobweb thread, which is picked up by the wind, carrying the spiders over long distances. This is how the species spreads. The web is used to catch prey. Many spiders build a trapping web (Fig. 303, 1). Even mating behavior is not complete in spiders without a web. During the breeding season, male spiders make a web "hammock" into which they release a drop of sperm. The male then crawls under the hammock and fills his seminal pods on the pedipalps with sperm. Seed capsules play the role of copulatory organs, with the help of which the spider injects sperm into the female genital opening.

Only two-lung spiders live on the territory of our country, about 1500 species. The most characteristic representatives among spiders are: house spider (Tegenaria domestica), cross-spider (Aganeus diadematus, Fig. 303), tarantula (Lycosa singoriensis), silver spider (Argyroneta aduatica).

The house spider lives in a human dwelling and stretches horizontal cobwebs in which it catches flies and other insects. Spider-cross - more large view, with a characteristic white cross pattern on the abdomen. Its vertically stretched nets can be seen on the walls of houses, fences, between tree branches. The house spider and the cross are among the web spiders that build nets - a trapping net in which prey is entangled.

A special group of spiders is formed by wolf spiders, which pursue prey on the go. They find shelter in special minks dug in the ground and lined with cobwebs. They have long legs and a narrow abdomen. These spiders include a tarantula that lives in the southern regions of our country. The bite of a tarantula causes painful swelling in a person, but does not pose a mortal danger to him.

Among all spiders, only one poisonous spider is dangerous to humans - karakurt (Latrodectus tredecimguttatus, Fig. 304), found in the dry steppe regions of Ukraine, the Volga region, the Caucasus and Central Asia. This is a medium-sized spider (1.5 cm), black with red spots. It lives in earthen burrows and spreads cobwebs on the surface of the soil, in which orthopterous insects usually come across. Its poison is dangerous to horses and humans, but not dangerous to sheep and pigs. The female karakurt is larger than the male and, as a rule, eats it after mating, therefore the karakurt is popularly called the "black widow".

Of biological interest is the silver spider, which lives in a web bell under water. The bell spider fills with air. The spider brings air bubbles on a fluffy abdomen that is not wetted by water. When a silver spider dives deep from the surface of the water, its abdomen is covered with a layer of air and therefore it seems silver.

Large tarantulas are common in the tropics (Fig. 305).

There are a lot of spiders in all tiers of land biocenoses, and they, as predators, play a positive role in regulating the number of herbivorous insects.

The order of acariform mites is the most numerous and includes more than 15 thousand species. These are very small forms (0.2-0.3 mm). In primitive representatives of the order, the anterior part of the cephalothorax is fused and forms a department - the proterosome, consisting of an acron and four segments. The three posterior segments of the cephalothorax are free and, together with the six abdominal segments and the telson, form the second part of the body, the hysterosome. On the proterosome are pincer-shaped chelicerae, flagellate pedipalps, and two pairs of walking legs. On the hysterosome are two posterior pairs of walking legs and abdominal appendages. The rudiments of the ventral legs on the 5th-7th segments form the genital covers, between which there is a genital cone with a genital opening. Under the floor covers there are three pairs of coxal organs in the form of thin-walled bags. Primitive acariform mites have skin respiration. In evolutionarily advanced forms, the body is fused, there are tracheae, and on different segments in different families. Reproduction is spermatophoric. Development with anamorphosis. Fig. 1. 305. Tarantula spider Poecilotheria regalis (according to Millo)

The family of thyroglyphoid mites, or barn mites, causes significant damage to grain, flour and other food products. These include ticks: flour, cheese, onion and wine. In nature, thyroglyphoid mites live in soil, fungi, decaying matter, bird nests, and mammalian burrows. Thyroglyphoid mites survive unfavorable conditions in the phase of a resting nymph covered with dense chitin (hypopus). Hypopuses withstand drying, freezing. Once in favorable conditions, the hypopuses become active and give rise to a new colony of ticks.

Some groups of ticks are herbivores. This is a family of gall-forming, spider mites. Among them are many pests of cultivated plants. For example, a cereal mite is a pest of crops, a spider mite is a pest of fruit trees. Many ticks live in the soil (red heifers), in fresh waters (Fig. 306, B).

Rice. 306. Ticks (from Lang, Matveev, Berlese, Pomerantsev): A - armored mite Galumna mucronata, B - feather mite Analgopsis passermus, C - water mite Hydrarachna geographica, D - four-legged mite Enophyes, E - itch itch Sarcoptes scabiei, E - Demodex folhculorum, G - cadaveric mite Poecilochirus necrophon, H - ixodid tick Dermacentor pictus

The detachment is characterized by the formation of a complex shell. In some forms, the anterior part of the cephalothorax, corresponding to the acron and three segments, is separated from the rest of the body by a suture. But in many species, all parts of the body are fused into a solid shell. Embryonic development of ixodid ticks shows that initially the cephalothorax is formed from the acron and six segments with six pairs of limbs. The seventh segment of the cephalothorax forms a transition zone on the border with the abdomen. The abdomen is formed from merged six large segments and 2-3 rudimentary ones.

Ixodid ticks have a solid flat body. The oral apparatus forms a "head" (gnathema) and consists of cutting chelicerae, to which jointed pedipalps adjoin on the sides, forming something similar to a case. The composition of the oral apparatus also includes a hypostome - an outgrowth of the pharynx with chitinous teeth. The tick bites through the skin with chelicerae and inserts a hypostome into the wound, which is anchored with teeth. A sucking tick is therefore very difficult to remove from the skin. If you tear it off by force, then its head remains in the skin, and this can cause inflammation. Therefore, it is recommended to lubricate the sucking tick with kerosene or oil, and it will disappear by itself. This is explained by the fact that, having lubricated the tick with oil, we clog its respiratory openings and the tick weakens without breathing, relaxes the muscles and falls off.

Ixodid ticks live in the soil and climb plants. In the process of development, most ixodid ticks change hosts. So, nymphs I hatched from eggs attack small rodents, lizards, chipmunks. After drinking blood, they fall off. After another molt, they attack other prey of the same species. Adult ticks usually feed on the blood of large mammals (ungulates, dogs) and humans. Males are usually half the size of females. Females can only lay eggs by sucking blood. Ticks can starve for a long time. They attack a person from trees and from the surface of the soil. AT eastern regions In the taiga zone of our country, the taiga tick (Ixodes persulcatus) is the most common. In the European part of the country, the dog tick (Ixodes ricinus) is the most common. About 50 species of ixodid ticks are known in our country. They carry pathogens dangerous diseases: encephalitis, tularemia, piroplasmosis, typhoid fever.

the disease is carried by carriers - blood-sucking ticks from animals - carriers of the infection (reservoir) to other healthy animals and humans. A person who enters the focal zone of the spread of infection is at risk of the disease. We have a network of medical and veterinary services that detects outbreaks of dangerous diseases carried by ticks. In these areas, anti-infective vaccinations are mandatory.

Detachment Ticks-harvesters (Opiliocarina). It is noteworthy that the harvest mites have a segmented body: the last two segments of the cephalothorax are free and the abdomen of eight segments. They have four pairs of stigmas on abdominal segments 1-4. The chelicerae are claw-shaped.

Habitat, structure and lifestyle.

Arachnids include spiders, ticks, scorpions and other arthropods, more than 35 thousand species in total. Arachnids have adapted to life in terrestrial habitats. Only some of them, for example, the silver spider, passed into the water for the second time.

The body of arachnids consists of a cephalothorax and usually a non-segmented abdomen or fused. There are 6 pairs of limbs on the cephalothorax, of which 4 pairs are used for locomotion. Arachnids do not have antennae or compound eyes. They breathe with the help of lung bags, trachea, skin. The largest number of arachnid species are spiders and mites.

Spiders

settled the most various places a habitat. In sheds, on fences, branches of trees and shrubs, openwork wheel-shaped networks of a spider-cross are common, and in their center or not far from them are the spiders themselves. These are females. On the dorsal side of their abdomen, a pattern resembling a cross is noticeable. Males are smaller than females and do not make trapping nets. In residential premises, sheds and other buildings, a house spider is common. He builds a trapping net in the form of a hammock. The silver spider makes a cobweb nest in the water in the form of a bell, and around it it pulls trapping cobweb threads.

At the end of the abdomen are arachnoid warts with ducts of the arachnoid glands. The substance released in the air turns into spider webs. When building a trapping web, the spider, using the comb-like claws of its hind legs, connects them into threads of different thicknesses.

Spiders are predators. They feed on insects and other small arthropods. The spider grabs the caught victim with its tentacles and sharp upper jaws, injects a poisonous liquid into the wounds, acting as digestive juice. After a while, he sucks out the contents of the prey with the help of a sucking stomach.

The complex behavior of spiders associated with the construction of trapping webs, feeding or reproduction is based on a multitude of successive reflexes. Hunger causes a reflex of searching for a place to build a trapping net, the found place serves as a signal for highlighting the web, fixing it, etc. Behavior that includes a chain of successive innate reflexes is called instinct.

Ticks

scorpions

Predators. They have a long segmented abdomen, on the last segment of which there is a stinger with ducts of poisonous glands. Scorpions catch and hold their prey with tentacles, on which claws are developed. These arachnids live in hot regions (in Central Asia, in the Caucasus, in the Crimea).

The meaning of arachnids.

Spiders and many other arachnids exterminate flies and mosquitoes, which are of great benefit to humans. Many birds, lizards and other animals feed on them. There are many spiders that harm humans. The bites of a karakurt living in Central Asia, the Caucasus, and the Crimea cause the death of horses and camels. For a person, scorpion venom is dangerous, causing redness and swelling of the bitten place, nausea and convulsions.

Soil mites, processing plant residues, improve the structure of the soil. But grain, flour and cheese mites destroy and spoil food supplies. Herbivorous mites infect cultivated plants. Scabies mites in the upper layer of human skin (usually between the fingers) and animals gnaw through passages, causing severe itching.

The taiga tick infects humans with the causative agent of encephalitis. Penetrating into the brain, the pathogen affects it. Taiga ticks get encephalitis pathogens by feeding on the blood of wild animals. The causes of the disease with taiga encephalitis were clarified in the late 30s by a group of scientists headed by academician E.N. Pavlovsky. All people working in the taiga are given anti-encephalitis vaccinations.

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Spiders ... What do we know about spiders, for many they cause fear, for many spiders cause a feeling of disgust. On our site you will get acquainted with some types of spiders. We will tell you about what varieties of spiders are, what makes them remarkable. In addition, we will dispel some of the myths that in our minds are quite strongly associated with spiders. Also, we will give you some helpful tips on how to get rid of spiders in your garden or home.

Spiders were the first among the earliest animals to live on earth. Despite the fact that the age of the life of spiders on the planet is quite significant, spider fossils are quite rare. According to historians, biologists and archaeologists, the first spiders on our planet appeared about four hundred million years ago. The ancestors of modern spiders were an arachnid, thick enough large sizes. For a fairly long period of time, this arachnid insect lived in the water. The first ancestors, which were already similar in body structure, and in other ways, to modern spiders were Attercopus fimbriungus (Attercopus fimbriungus). Fossils of Attercopus fimbriungus (Attercopus fimbriungus) have been found by archaeologists, although, as we said above, the number of such finds is quite small. Attercopus fimbriungus (Attercopus fimbriungus) lived approximately three hundred and eighty million years ago, that is, approximately one hundred and fifty million years ago before the first dinosaurs appeared on the planet. Most of early spiders, the so-called segmented spiders, that is, those that already had a fairly well-formed abdomen, belonged to the Mesothelae variety (Mesoselai). The Mesothelae group (Mesoselai) differed in that the place from which they unwound the web was in the middle of their abdomen, and not at the end of the abdomen, like their modern "relatives". It is likely that such distant ancestors of spiders lived on earth, they were predators, lived in giant thickets, fern forests. These spiders lived around the middle of the Paleozoic. Apparently the Mesothelae were predators and preyed on other primitive insects such as cockroaches, roofers and centipedes. The web, quite possibly, was used simply as protective coating for eggs, later, it is possible that the web was also used to create simple nets arranged on the ground, as well as to create a so-called hatch or loophole. Thanks to the development of evolution, including the evolution of plants, the life of spiders began to change. Spiders with a weaving device at the end of the abdomen, and these spiders were called Opisthothelae (Opissosalai) appeared more than two hundred and fifty million years ago. These spiders could already weave more complex networks, which are real labyrinths. Thus, smaller insects directly on the ground fell into such complicated nets, and nets could also be found in the foliage. With the onset jurassic(approximately one hundred and ninety-one - one hundred and thirty-six million years ago), during this historical period, dinosaurs already walked on our planet, air networks that skillfully weaved by spiders were already designed to trap and, accordingly, catch, that incredible number of insects that were just teeming with foliage. Approximately in the same way, with an increase in the total number of spiders on the planet, the spiders themselves became quite easy prey, thereby, the spiders were forced to adapt to the new habitat. To date, there is a sufficient amount of mined fossils, the age of which is determined as the Tertiary period. According to the analysis of fossil data, spiders can be seen as if they were trapped in the resin of trees. So, according to these fossils, the species diversity of spiders that we can observe now is quite consistent with the species diversity of these insects, which existed about thirty million years ago.

Most spiders are small, featureless arthropods that are harmless to humans. Their beneficial role in maintaining insect populations far outweighs the danger from the few spiders that occasionally bite humans. Only a few varieties of spiders are venomous; spiders and insects are waging a fairly serious fight, the preponderance of which is more often on the side of predators.

Tarantulas, jumping spiders, and some other species scare people, the latter mistakenly believe that they are serious danger. Although these spiders are large, hairy, and unattractive in appearance, their sting is generally less dangerous than a bee sting. True, if you are allergic to spider venom, any spider bite will cause you a serious reaction. Many people are afraid of spiders, however, knowing how to distinguish harmless animals from truly dangerous ones, how to prevent them from entering the house, and how to protect yourself from those who can really harm, you can save yourself from panic fear, or at least reduce it.

The main product that spiders eat is insects, but large varieties They can also attack small birds and animals.

Are recluse spiders the most dangerous?

While only a few of the hermits are actually venomous to humans, it is best to view the entire species as potentially dangerous.

A small digression: we must not forget that spiders are not insects, they are closer in structure to crabs and crayfish. Hermit spiders choose garages, woodpile, basements, etc. as their habitat, often settling near human dwellings and inside them. They are most active at night (like many spiders), then the insects at home also wake up, and eight-legged creatures declare a hunt for them. They often bite people in their sleep, most likely when a person accidentally hits them, causing a reasonable self-defense reaction. Others get bitten when they take clothes that for a long time hung untouched in a closet, and in which the hermits settled.

poisonous spiders

In reality poisonous spiders are not as big of a threat as is commonly believed. The existing antidote for the bites of various types of spiders is very effective today, and deaths from a bite are very rare, for example, in the USA, an average of 4 people die per year. However, spider venom can cause severe skin lesions that must be urgently treated and carried out for long care procedures. All spiders use venom to kill their victims after they are caught in webs or captured by the spiders through other means. Poisonous spiders, on the other hand, have a more serious poison, aimed at immobilizing and killing large victims, and used by them not only for food, but also for self-defense. The likelihood of death or serious injury from a bite is very small - however, in any case, it is better to consult a doctor to avoid serious consequences.

tarantula spiders

Tarantulas have long taken their place as pets with extreme breeders. In this they are helped by an attractive appearance, variegated coloration, low requirements for nutrition and care, etc. They are recommended for those who want to have a spider at home for the first time. They are also quite long-lived pets, the average life expectancy is calculated in a couple of decades (representatives of the weaker sex). Tarantulas are tropical inhabitants, who have now gained popularity in our country as pets. As the name implies, tarantulas, at least some of their varieties, feed not just on insects, but also on birds. Of course, tarantulas, like other spiders, believe that insects are quite acceptable food for them, but they need a lot more of it. Tarantulas are large creatures with powerful mandibles and strong poison; their method of hunting can be called active, since they do not wait until the animal is entangled in the web, but attack it from an ambush.

house spiders

Several varieties of spiders are often found in the household. With rare exceptions, they are quite harmless, being in the corners and building networks there, some of them are even beneficial because they feed on household pests (flies, moths). Sometimes house spiders bite people, but in most cases their bites are not dangerous. But, if your home spiders are a black widow, a hermit, and other species that are deadly, you need to get rid of such a terrible neighborhood.

What can you do about it?

To keep spiders out of the house, you can use mechanical methods - kill them with your hands, a newspaper, a broom, or suck them out with a vacuum cleaner. Domestic spiders are also afraid of chemical sprays based on boric acid, chlorpyrifos, etc. If you patch up cracks in your home, increase the sealing of your windows, or pick up trash outside your home, house spiders are unlikely to get to you. For prevention, you can also use special sprays designed for spraying on the street. If you have been bitten by a spider, and you do not know which species it belongs to, it is better to visit an infectious disease specialist.

Dream interpretation: spiders

Arachnophobia, the fear of spiders, is the most well-known phobia among Americans, and quite common among us. Many people say that these hairy eight-legged creatures disgust them. If you look into the dream book, spiders dream of many situations that await you in the future, but why do they appear in your dreams? Most likely, this is an expression of your subconscious attitude towards them, but the image of a spider is much deeper than just getting goosebumps from its appearance. If you have ever read any of the African tales, you may have noticed that spiders are cunning, treacherous creatures often associated with deceit. This is most likely due to their type of diet. Very often, having seen a dream, we take a dream book, spiders on it (in various interpretations) are just a warning about the danger of falling into the network of deception. Another association associated with spiders comes from their ability to weave beautiful, intricate webs. The well-known myth of Arachne, who turned into a spider, also testifies to this. If in a dream you see a web, it is quite possible that this means that your creative impulses are being ignored, spiders weaving a web indicate that inspiration is right in front of you. When considering the symbolic meaning of spiders, one cannot lose sight of the cannibalistic tendencies of many females who kill partners after mating. It can be said without looking into the dream book that spiders are feminine energy inside of us, and if you have dreams about the murder of your partner by a spider, it means that serious changes are coming in your life. Spiders, unlike insects, do not have antennae (antennae) and jaws. The body is covered with an external skeleton (exoskeleton) and consists of two sections - the cephalothorax, formed by the merged head and chest, and the abdomen. At the anterior end of the cephalothorax are simple eyes, the location of which serves as an important classification feature. Most spiders have four pairs. The cephalothorax bears six pairs of limbs. On the front of the head are two downward-pointing, jaw-like chelicerae, each ending in a sharp claw. Poison glands located in these limbs open on it. The second pair are pedipalps, used as palps and grasping structures. In mature males, their ends are modified and are used for mating. Between the bases of the pedipalps is a small mouth opening. All spiders, unlike insects, have four rather than three pairs of walking legs. The last segment of each of them bears at least two claws, and in some species there are many more. The arachnoid glands open on the underside of the abdomen, usually with six arachnoid warts. In front of them are small respiratory openings - spiracles, or stigmas. On the abdomen are modified organs, spinnerets, used in silk spinning. Breathing holes in the abdomen lead to the so-called book lungs (named for their layered structure) or plug system (trachea) for air.

The digestive system of spiders is adapted exclusively to the digestion of liquid food, because insects capture their prey and then suck the liquid out of them. Spiders have a fairly complex brain, larger or smaller in certain parts, depending on whether the animal locates prey mainly through contact or sight. With a bite, spiders paralyze prey: this is how their poison acts on the victim's nervous system. They can only eat liquid food, since the mouth opening of spiders (in the form of a tube) is very narrow. Therefore, spiders inject a special substance inside the prey, which acts like digestive juice, corroding tissues. Then they suck out the victim, leaving only an empty skin. Such digestion is called extraintestinal. All spiders are carnivorous insects by nature, and most of them live on their prey. They can survive for long periods without food. Some spiders have been kept alive for over two years without food. Spiders hunt day and night. All are well equipped with sensory hairs on their bodies and legs, they can easily detect the slightest change in air currents, indicating the movement of prey. Spiders will often feed on other spiders. Most hunters will attack prey smaller than themselves and will run away from prey larger than themselves. Those that have well developed jaws (chelicerae) tear open their prey and drink the digestive juices from it. Those in which the chelicerae are not very developed inject poison and then suck out the juice. The feeding process is slow, for a large fly spider it can take up to 12 hours. Since the soft cuticle of the spider's abdomen is stretched when food is absorbed, but when the maximum amount of liquid is reached, further stretching is impossible. None of the harder sclerotized parts are capable of increasing in size because, as in all insects, the skeleton is on the outside. Thus, the old spider must shed. The old cuticle splits and makes room for a softer cuticle that strengthens over time. Nymphs molt frequently, every few days during which their size increases, this does not happen with mature spiders. The interval between molts increases with the age of the spider. The smaller species shed about five times less than the larger spiders. Sometimes shedding doesn't go according to plan, legs get stuck, etc. Then the spider dies, or it may break its legs to set them free, they are very susceptible at this stage.

Recently, scientists from Simon Fraser University in Canada described another example of a surprisingly complex behavior of spiders that does not fit in with the image of "primitive" tiny animals. It turned out that male black widows deliberately destroy the web of females in order to reduce the number of potential rivals in mating season. Like not-too-honest businessmen ripping off competitors' ads, they wrap the web of females in special cocoons so that the pheromones it contains cannot spread through the air. We decided to look at other similar examples of complex behavior that show that spiders are not at all as simple as people think they are.

Western black widow males Latrodectus hesperus, in the course of courting a female, bundles are made from flaps of her web, which are then braided with their own web. The authors of an article published in animal behavior, suggested that this should reduce the amount of female pheromones that are released into the air from their webs and can attract rivals. To test this hypothesis, the scientists took four different kind cobwebs woven by females in cages in the laboratory: partially folded by males, partially cut with scissors, cobwebs with artificially added pieces of male cobwebs and intact cobwebs. The females were removed from all the webs, and then the cages with the webs were taken to the coast of Vancouver Island, where black widows live, to find out how many males various specimens will attract.

After six hours, the intact webs attracted more than 10 male black widows. Webs partially rolled up by other males turned out to be three times less attractive. Interestingly, however, the nets damaged by scissors and nets with artificially added male cobwebs attracted the same number of males as intact nets. That is, neither the cutting out of pieces nor the addition of the male's web in itself affected the attractiveness of the web. As scientists conclude, in order for the web to become less attractive to rivals, both manipulations are needed: targeted cutting of sections of the web marked with female pheromones and wrapping these sections with the web of males, which serves as a barrier to the spread of female pheromones. The authors also suggest that some compounds contained in the web of males can change the signals emitted by female pheromones.

Another example of the cunning of spiders is the behavior of males of another species of black widows, Lactrodectus hasselti. The females of these Australian spiders, which are noticeably larger than males, require at least 100 minutes of grooming before mating. If the male is lazy, the female will most likely kill him (and eat him, of course). After reaching the threshold of 100 minutes, the probability of killing is greatly reduced. However, this does not give any guarantees: even after a 100-minute courtship, a successful male in two out of three cases will be killed immediately after mating.

Spiders know how to deceive not only their women, but also predators. Yes, orb-weaving spiders Cyclosa ginnaga they disguise themselves as bird droppings, weaving a dense white “blot” in the center of their web, on which the silver-brown spider itself sits. To the human eye, this blob with a spider sitting on it looks exactly like bird droppings. Taiwanese scientists decided to make sure that this illusion also works on those for whom it is, in fact, intended - predatory wasps that prey on orb-weaving spiders. To do this, they compared the spectral reflectances of the body of a spider, "blots" from the web and real bird droppings. It turned out that all these coefficients are below the color recognition threshold for predatory wasps - that is, the wasps really do not see the difference between a camouflaged spider and bird droppings. To test this result experimentally, the authors painted the “blobs” on which the spiders sat black. This significantly increased the number of wasp attacks on spiders - spiders sitting on an intact web were still ignored by the wasps.

Orb-weaving spiders are also known for making “stuffed animals” of themselves from pieces of leaves, dry insects and other debris - real self-portraits with a body, legs and everything else that a spider is supposed to have. These stuffed spiders are placed on the web to distract predators, while they themselves hide nearby. Like fake bird droppings, stuffed animals have the same spectral characteristics as the body of the spider itself.

The Amazonian orb-weaving spiders went even further. They learned how to create not just stuffed animals, but real puppets. Having made a fake spider out of garbage, they make it move by pulling the strings of the web. As a result, the stuffed animal not only looks like a spider, but also moves like a spider - and the owner of the puppet (which, by the way, is several times smaller than his self-portrait) hides behind it at this time.

All these examples are, of course, wonderful, but they do not say anything about the "mind" of spiders and their ability to learn. Can spiders "think" - that is, find non-standard ways out of non-standard situations and change their behavior depending on the context? Or is their behavior based only on patterned behavioral responses - as is commonly expected from "lower" animals with small brains? It seems that spiders are still smarter than is commonly believed.

One of the experiments showing that spiders are capable of learning - that is, adaptive behavior change as a result of experience - was carried out by a Japanese researcher on orb weaving spiders. Cyclosa octotuberculata. These spiders weave a "classic" circular web, consisting of adhesive spiral and non-adhesive radial filaments. When the prey hits the sticky spiral filaments, its vibrations are transmitted along the radial filaments to the spider sitting in the center of the web. Vibrations are transmitted the better, the stronger the radial threads are pulled - therefore, the spiders, in anticipation of the victim, alternately pull the radial threads with their paws, scanning different sectors of the web.

In the experiment, the spiders were brought to the laboratory, where they were recreated in their natural habitat, and given time to weave a web. After that, the animals were divided into two groups, each member of which was given one fly per day. However, in one group, the fly was always placed in the upper and lower sections of the web (the "vertical" group), and in the other, in the side sections (the "horizontal" group).

Another experiment proving that the behavior of spiders is determined not only by template instinctive programs is shown in the famous film by Felix Sobolev " Do animals think(You should definitely watch it in its entirety.) In an experiment conducted in a laboratory (but, unfortunately, not published in a peer-reviewed journal), a thousand threads were lowered onto a thousand spider webs, partially destroying the webs. 800 spiders simply left the destroyed webs, but the rest of the spiders found a way out. 194 spiders gnawed the web around the thread - so that it hung freely, without touching the nets. Another 6 spiders wound the strings and firmly glued them to the ceiling above the cobweb. Can this be explained by instinct? With difficulty, because the instinct should be the same for all spiders - and only some of them "thought of" something.

As befits intelligent creatures, spiders are able to learn from other people's mistakes (and successes). This was shown by an experiment conducted by American scientists on male wolf spiders. Spiders brought from the forest to the laboratory were shown several videos in which another male performed a courtship ritual - he danced, stamping his foot. Looking at him, the audience also began a ritual dance of courtship - despite the fact that the female was not on the video. That is, the spiders "assumed" the presence of the female, looking at the dancing male. By the way, the video, in which the spider just walked through the forest, and did not dance, did not cause such a reaction.

However, this is not what is curious here, but the fact that the male spectators diligently copied the dance of the male actor. Comparing the characteristics of the dance - the speed and number of kicks - between the actors and the audience, the scientists found their strict correlation. Moreover, the audience tried to outdo the spider in the video, i.e. stomp their feet faster and better.

As the authors note, such copying of someone else's behavior was previously known only in more "intelligent" vertebrates (for example, in birds and frogs). And no wonder, because copying requires a great plasticity of behavior, which is generally uncharacteristic for invertebrates. It is curious, by the way, that the earlier experiment of the authors, which used "naive" spiders grown in the laboratory and had never seen courtship rituals before, did not give similar results. This further indicates that the behavior of spiders can change with experience, and not just determined by template behavioral programs.

An example of an even more complex type of learning is reversal learning, or reshaping a skill. In other words, retraining. Its essence is that the animal first learns to associate the conditioned stimulus A (but not B) with the unconditioned stimulus C. After some time, the stimuli are reversed: now not A, but B is associated with stimulus C. The time it takes for the animal to relearn , is used by scientists to assess the plasticity of behavior - that is, the ability to quickly respond to changing conditions.

It turned out that spiders are capable of this type of learning. This was shown by German researchers using the example of Marpissa muscosa jumping spiders. In plastic boxes they placed two LEGO bricks - yellow and blue. Behind one of them was hidden a reward - a drop of sweet water. The spiders released at the opposite end of the box had to learn to associate either the color of the brick (yellow or blue) or its location (left or right) with the reward. After the spiders were successfully trained, the researchers proceeded with a retraining test: swapping either the color, or the location, or both at once.

The spiders were able to relearn, and surprisingly quickly: it only took one attempt for many to learn to associate the reward with the new stimulus. Interestingly, the subjects differed in learning abilities - for example, with an increase in the frequency of training, some spiders began to give correct answers more often, while others, on the contrary, began to make more mistakes. Spiders also differed in the type of key stimulus they preferred to associate with the reward: some found it easier to “relearn” the color, and others the location of the brick (although most still preferred the color).

The jumping spiders described in the last example are generally remarkable in many ways. A well-developed internal hydraulic system allows them to lengthen their limbs by changing the pressure of the hemolymph in them (an analogue of blood in arthropods). Thanks to this, jumping spiders are able (to the horror of arachnophobes) to jump a distance several times their body length. They also, unlike other spiders, easily crawl on glass - thanks to tiny sticky hairs on each foot.

In addition to all this, horses also have unique vision: they distinguish colors better than all other spiders, and in terms of visual acuity they surpass not only all arthropods, but in some aspects even vertebrates, including individual mammals. The hunting behavior of jumping spiders is also very complex and interesting. As a rule, they hunt in the manner of a cat: they hide in anticipation of prey and attack when it is close enough. However, unlike many other invertebrates with their stereotypical behavior, jumping spiders change their hunting technique depending on the type of prey: they attack large prey only from behind, and small ones - as they have to, they chase a fast-moving prey themselves, and wait for a slow one in ambush .

Perhaps the most surprising in this respect are the Australian jumping spiders. During the hunt, they move along the branches of a tree until they notice the victim - the orb-web spider, which is capable of self-defense and can be quite dangerous. Noticing the prey, the jumping spider, instead of heading straight for it, stops, crawls to the side and, having studied the surroundings, finds a suitable point above the victim's web. Then the spider gets to the chosen point (and often for this he has to climb another tree) - and from there, releasing a cobweb, jumps onto the victim and attacks it from the air.

This behavior requires a complex interaction between different brain systems responsible for image recognition, image categorization, and action planning. Planning, in turn, requires a large amount of working memory and, as scientists suggest, involves compiling an “image” of the chosen route long before the start of movement along this route. The ability to make such images has so far been shown only for very few animals - for example, for primates and corvids.

Such complex behavior is surprising for a tiny creature with a brain less than one millimeter in diameter. Therefore, neuroscientists have long been interested in the jumping spider, dreaming of understanding how a small handful of neurons can provide such complex behavioral responses. However, until recently, scientists could not get to the brain of a spider to record the activity of neurons. The reason for this is all in the same hydrostatic pressure of the hemolymph: any attempts to open the spider's head led to a rapid loss of fluid and death.

Recently, however, American scientists finally managed to get to the brain of a horse spider. Having made a tiny hole (about 100 microns), they inserted the thinnest tungsten wire into it, with which they were able to analyze the electrophysiological activity of neurons.

This is great news for neuroscience, because the jumping spider brain has some very research-friendly properties. Firstly, it allows you to separately study different types of visual signals by closing the spider's eyes in turn, of which it has as many as eight (and most importantly, these eyes have different functions: some scan stationary objects, while others react to movement). Secondly, the brain of a jumping spider is small and (finally) easily accessible. And third, this brain controls behavior that is surprisingly complex for its size. Research in this area is just beginning today, and in the future, the jumping spider is sure to tell us a lot about how the brain works - including our own.

Sofia Dolotovskaya