The first ancestors of the current specimens appeared on Earth about 400 million years ago. They originated from marine organisms of the chelicerae subtype. The oldest ancestor of modern spiders found in the fossil record is Attercopus fimbriunguis, which is 380 million years old.
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Spiders are arthropods.
These are invertebrates whose body is divided into segments and has an external skeleton. Spiders are classified as arachnids, which include about 112 animal species.
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More than 49800 species of spiders have been described, divided into 129 families.
The division has not yet been completely systematized, since over 1900 different classifications of these animals have appeared since 20.
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The body of spiders consists of two segments (tagmas).
This is the cephalothorax and abdomen, connected by a column. In the anterior part of the cephalothorax there are chelicerae, behind them there are pedipalps. They are followed by walking feet. The abdominal cavity contains organs such as the heart, intestines, reproductive system, cotton glands and spiracles.
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The size of spiders varies significantly depending on the species.
Smallest species Pato Digua native to Colombia, whose body length does not exceed 0,37 mm. The largest spiders are tarantulas, which can reach 90 mm in length and a leg span of up to 25 cm.
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All legs grow from the cephalothorax. Spiders have five pairs of them.
These are a pair of pedipalps and four pairs of walking legs.
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If there are any protrusions on the spider's abdomen, these are silk glands.
They are used to spin silk thread, from which spiders build their webs. Most often, spiders have six silk glands, but there are species with only one, two, four or eight. Silk nets can be used not only to create webs, but also to transfer sperm, build cocoons for eggs, wrap prey, and even create balloons/parachutes so they can fly.
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Each perineal leg consists of seven segments (starting from the body, these are: coxa, trochanter, femur, patella, tibia, metatarsus and tarsus).
The leg ends in claws, the number and length of which vary depending on the type of spider. Spiders that spin webs usually have three claws, while spiders that actively hunt usually have two.
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Chelicerae consist of two or three segments.
They end in fangs, with which the spider tears the body of the victim and also defends itself. In many species they end with the mouth of poison glands.
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The pedipalps consist of six segments.
They lack a metatarsal segment. In males, the last segment (tarsus) is used for reproduction, and the first (coxa) in both sexes is modified to make it easier for the spider to eat.
10
They usually have eight eyes equipped with lenses. This distinguishes them from insects, which have compound eyes. The vision of most spiders is not very well developed.
However, this is not the rule, as there are families of spiders with six (Haplogynae), four (Tetablemma) or two (Caponiidae). There are also species of spiders that have no eyes at all. Some pairs of eyes are more developed than others and serve different purposes, for example the primary eyes of jumping spiders are capable of color vision.
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Since spiders do not have antennae, their legs took over their role.
The bristles covering them have the ability to capture sounds, odors, vibrations and air movements.
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Some spiders use environmental vibrations to find prey.
This is especially popular among web-spinning spiders. Some species can also locate prey by detecting changes in air pressure.
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The eyes of Deinopis spiders have phenomenal properties by the standards of spiders. Currently, 51 species of these spiders have been described.
Their central eyes are enlarged and point straight ahead. Equipped with superior lenses, they cover a very large field of view and collect more light than the eyes of owls or cats. This ability is due to the absence of a reflective membrane. The eye is poorly protected and is seriously damaged every morning, but its regenerative properties are so outstanding that it quickly recovers.
These spiders also do not have ears and use the hairs on their legs to “listen” for prey. Thus, they can detect sounds within a radius of two meters.
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Their circulatory system is open.
This means that they do not have veins, but the hemolymph (which functions as blood) is pumped through arteries into the body cavities (hemoceles) surrounding the internal organs. There, gas and nutrients are exchanged between the hemolymph and the organ.
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Spiders breathe through lungs or windpipes.
Pulmonary tracheae evolved from the legs of aquatic arachnids. The trachea, in turn, are bulges in the walls of the spiders' bodies. They are filled with hemolymph, which is used to transport oxygen and performs an immune function.
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Spiders are predators.
Most of them eat only meat, although there are species (Bagheera kiplingi) whose diet consists of 90% plant ingredients. The young of some species of spiders feed on plant nectar. There are also carrion spiders that feed mainly on dead arthropods.
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Almost all spiders are poisonous.
Although there are so many of them, only a few species pose a threat to humans. There are also spiders that do not have venom glands at all, these include spiders from the family Uloborides.
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Work is underway to use the venom of some spiders to create an environmental pesticide.
Such a toxin will be able to protect crops from harmful insects without polluting the natural environment.
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Digestion occurs both externally and internally. They eat only liquid food.
First, digestive juices are injected into the prey's body, which dissolves the prey's tissues, and the next stage of digestion occurs after the spider has consumed these tissues within the digestive system.
20
To make up for the lack of proteins, spiders eat the webs they weave.
Thanks to this, they are able to weave a new, fresh one without the need for hunting, when the old web is no longer suitable for this purpose. A great example of waste recycling among animals. A similar mechanism occurs in shrimp, which eat their shell during molting.
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Spiders are not capable of biting their prey.
Most of them have a straw-like device in their mouthparts that allows them to drink dissolved prey tissue.
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The excretory system of spiders consists of the ileal glands and Malpighian tubules.
They capture harmful metabolites from the hemolymph and send them to the cloaca, from where they exit through the anus.
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The vast majority of spiders reproduce sexually. Sperm is not introduced into the female’s body through the genitals, but is stored in special containers located on the pedipalps.
Only after these containers are filled with sperm does the male go in search of a partner. During copulation, they penetrate the female's external genitalia, called the epiginum, where fertilization occurs. This process was observed back in 1678 by Martin Lister, an English physician and naturalist.
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Female spiders can lay up to 3000 eggs.
They are often stored in silk cocoons that maintain appropriate humidity. Spider larvae undergo metamorphosis while still in cocoons and leave them when they reach a mature body form.
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The males of some species of spiders have developed the ability to perform a very impressive mating dance.
This feature is characteristic of jumping spiders, which have very good vision. If the dance convinces the female, fertilization occurs, otherwise the male has to look for another partner, less demanding of sophisticated cat movements.
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A significant number of spiders experience cannibalism associated with the act of reproduction.
Most often, the male becomes the victim of the female, usually during or after copulation. Cases when a male eats a female are extremely rare. There are species in which up to ⅔ of the cases the male is eaten by the female. In turn, the roles of water spiders are reversed (Argyronethia aquatic), where males often eat smaller females and copulate with larger females. In spiders Allocosa brasiliensis males eat older females, whose reproductive abilities are no longer as good as those of younger ones.
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Cannibalism also occurs in newly hatched spiders.
They, in turn, eliminate the weakest siblings, thus gaining an advantage over others and giving themselves a better chance of reaching adulthood.
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Young spiders are naturally much more aggressive than adults, and from a developmental perspective this makes sense.
A spider that eats more food will grow larger as an adult. Therefore, we can assume that the larger the spider we encounter (in relation to representatives of its species), the more aggressive it is.
