Spider legs - features and purpose of arthropod limbs

External structure

The body structure of a spider may vary slightly depending on the species. The size of the arthropod can range from a few millimeters to 30 cm.

The spider's body is divided into a cephalothorax and abdomen, connected to each other by a stalk. These two sections are clearly distinguishable visually. The outer chitinous shell that covers the insect's body is called the exoskeleton.

It includes:

1. chitin.
2. Protein sclerotin.

The body parts of spiders are covered with a chitinous layer that protects the body from mechanical damage and drying out. The chitinous shell is not capable of changing its size, so the spider periodically changes it to a new one.

The abdomen is covered with more elastic skin, due to which it is able to significantly increase in size after a meal.

All the limbs of the spider are attached to the cephalothorax or prosoma. On the carapace (anterior part of the prosoma) there are several pairs of eyes. The sternum (lower part of the cephalothorax) contains the lower and upper lips. Immobile chelicerae are attached to them. They consist of one segment, to which movable sharp fangs are attached.

Venom ducts approach the fangs. On the sides of the prosoma there are coxae to which the limbs are attached. They are not protected by chitin, thanks to which the spider is able to move quickly and deftly.

Spiders have 6 pairs of limbs:

• 1 pair of chelicerae;
• 1 pair of pedipalps;
• 4 pairs of walking legs.

The pedipalps consist of 6 segments. They serve for orientation in space. Mature males develop cymbiums at their ends, with the help of which they fertilize females. In large species, the pedipalps are quite long, and therefore they are often mistaken for another pair of walking limbs.

Each walking leg consists of 7 segments connected by joints.

They have the following names:

1. paw.
2. Forefoot.
3. Shin.
4. Cup.
5. Hip.
6. Trochanter.
7. Basin.

The abdomen is also called opisthosoma or abdomen. At its end there are two processes, which are arachnoid appendages. Below them is the anus.

Zoologists explained the ability of spiders to crawl on any surface

Some spiders have a rather massive body, however, despite gravity, they can easily climb absolutely smooth vertical surfaces. Zoologists have puzzled over this secret for many years, and now they have discovered an interesting anatomical feature and behavioral cunning of arthropods that allows them to crawl on any surface.

Spiders have thousands of tiny hairs on the tips of their legs that create contact points. These hairs are very small and flexible, and therefore can catch on any minimal unevenness. At the molecular level, every surface, even the smoothest in appearance, has roughness and bulges that can only be grasped by very thin hairs.

“Because the hairs on spiders’ legs are also very flexible, they can catch on several parts of the surface at once. This provides additional stickiness,” explains study lead author Jonas Wolff, a biologist at the University of Kiel in Germany.

Spider of the species Cupiennius salei and its web

Unlike barnacles, which attach themselves to rocks or ship hulls for their entire lives, spiders only temporarily attach their legs to the surface on which they climb. Biologists call this ability dynamic attachment. The authors of the new study compare the process to putting stickers on a refrigerator.

“Unlike glue, which holds one surface to another for a long time, spider hairs stick to the bumps for just a second, after which the contact can be broken without much difficulty,” says Wolff, who has been studying this issue for many years.

As part of their experiment, scientists examined the abilities of spiders of the species Cupiennius salei. These arthropods generate enough adhesive force to keep them from falling, but are also able to quickly tear off their legs to instantly capture and consume prey.

As a rule, the attack on the victim lasts only a quarter of a second, after which the spider runs away at a speed of half a meter per second. For such manipulations, hairs must be torn off extremely quickly, says Wolff.

Initially, scientists assumed that the secret lay only in the hairs on the legs, but Wolff suspected that this was not the only feature of the spiders. He measured the force that the spider's body imparted to the glass, and it was equal to 97 milli-Newtons or 10 grams.

To capture prey, the spider moves its legs and thus weakens the sticky force that holds its legs on a vertical surface.

(photo by Shanthanu Bhardwaj/Flickr).

“It doesn’t sound very impressive, but that’s three or four times the weight of a spider’s body. Thus, you can hang a load from the spider’s body that is equal in mass, and the animal will not fall from a smooth vertical glass surface. In small individuals, this ratio is even higher, since the tips of their paws are even smaller relative to the volume of the body,” says the biologist.

To determine how each individual leg generates the key force, the researchers applied warm beeswax to the spiders' legs, depriving them of their ability to cling to hairs. The paws were “turned off” first one at a time, then in pairs, and then all at once. The scientists found that the force generated by opposing paws (such as the front left and back right) unlocked the arthropod's ability to attach to smooth glass.

When the opposite legs move apart, more friction is generated between the hairs and the surface, and due to this, the spider attaches its body more securely. But at the moment when it is necessary to tear off the paws and capture the prey, the arthropods reduce the distance between the limbs, and the stickiness decreases.

In their article published in the Journal of Experimental Biology, Wolff and his colleagues talk about their observations and calculations. The scientists also mentioned that people would not be able to resort to the same trick even if they had a Spiderman suit: a person is too heavy for such abilities.

Also on the topic: Geckos cope with wet surfaces until their feet get wet New patch will allow people to walk on walls Electricity helps spiders catch prey The mechanism of action of the venom of the brown recluse spider has been clarified Students calculated that a web can stop a train Scientists have invented a Spider-Man costume

Internal structure

The internal structure of the spider has the following features:

1. the spider has no skeleton. Muscles are attached to a collection of empty and tissue-filled cavities.
2. External digestion of food.
3. The spider does not hear sounds, but it is able to sense air vibrations.
4. There are organs that are responsible for the formation of the web.
5. Instead of blood, hemolymph circulates throughout the body. It contains copper and can be poisonous to some other animal species.

Endoskeleton

Inside the body there is a whole system of different organs that will serve as the spider’s skeleton.

They are called endoskeleton. It consists of the following parts:

1. apodem. Empty cavities that serve to attach muscles. A small depressed area is located in the center of the cephalothorax. It is to this that the sucking ventricle is attached with the help of muscles. There are several other small epidemics that are needed to connect the spider's muscles to the exoskeleton. Outwardly, they look like long stripes that run along the entire body of the animal.
2. Entosternum. In structure and functionality it resembles an apodeme. Only the cavities to which the muscles are attached are filled with tissue similar to cartilage.
3. Apophysis.

Nervous system and sensory organs

The nervous system is one of the most important components in the anatomy of a spider. It is she who transmits signals from receptors to the brain - the main organ that is responsible for the functioning of the entire body. It is located at the bottom of the prosoma.

It consists of upper and lower parts. The upper brain is responsible for processing information received from the senses. The lower brain is large.

It gives commands to the musculoskeletal system. It is in it that instincts and reflexes are formed. Also inside the brain are glandular bodies that are responsible for the production of hormones.

Nerve threads extend to all organs inside the cephalothorax. And only one of them goes into the abdomen through the stalk.

The following sense organs can be distinguished that help arthropods navigate in space:

1. eyes. At the beginning of the cephalothorax, above the chelicerae, there is a small mound. It is on it that several pairs of eyes are located. Spiders have poor eyesight, and therefore the eyes are not their main sense organ. A large number of species are nocturnal or burrowing, so they practically do not rely on vision.
2. Hairs. Located throughout the body. Most of them are associated with nerve endings. With the help of hairs, animals are able to detect vibrations in air and soil, smell and identify objects. One touch is enough for the spider to understand that it is food in front of it, and not something inedible.
3. Taste buds are located on the walls of the pharynx.
4. Lyre-shaped organs. These are small cracks covered with a thin film. They are filled with nerve endings and are found on the legs of the arthropod.
5. Tarsal organs. They are located on the pedipalps and the first two legs.

Digestive system

In spiders, the structure of the food system is due to the fact that their digestion of food occurs outside the body. The oral opening is located in the front of the cephalothorax between the chelicerae. The esophagus tube comes from it.

Through it, food enters the sucking ventricle. Through a short tube it is connected to the true ventricle. From here extends the small intestine, which goes through the stalk into the abdomen. The rectum ends with the anus.

The abdomen contains the Malpighian canals. These are thread-like organs of a spider that perform the same function as the kidneys in humans.

Using its fangs, the spider pierces the skin of the victim and injects gastric juice under it. The digestion process begins. The victim's tissues turn into a nutritious liquid. By contracting the sucking stomach, the spider draws food into itself.

With the help of stinging hairs on the chelicerae, it filters out large particles. Afterwards the food enters the true stomach. Partially digested, it rushes into the intestines. After the digestion process is completed, all remaining food and salt leave the body through the anus.

Circulatory and respiratory system

The spider's body is filled with a special liquid - hemolymph. The heart is located in the back of the abdomen. Outwardly, it looks like a long tube. The heart is placed inside a special cavity - the pericardium. The pericardium is equipped with a large number of nerve fibers.

It is they who cause the ligaments to contract, due to which hemolymph circulates throughout the animal’s body. There are four holes in the heart that act as valves.

Blood vessels run from the heart throughout the body. Arachnids have an open circulatory system. With each contraction of the pericardium, hemolymph rushes in several directions at once: forward, backward and to the sides. Hemolymph is capable of carrying oxygen throughout the body. Afterwards it seeps back into the vessels.

The spider has two pairs of lungs. They are located in the anterior part of the opisthosoma, not far from the cephalothorax. They consist of thin plates in which oxygen from the external environment replaces carbon dioxide.

Why do spiders appear in the car?

As already noted, the time of meeting the spider can play a determining role. So, if it happened in the morning, it means that a person expects experiences, sorrows and problems, in the afternoon - worries or great feelings, and in the evening - a gift or receiving a letter.

There are some signs about arthropods in the car

:

• If a spider crawls in a car, then it indicates material issues. It is important to take into account the direction of its movement. When it comes to rapprochement, the financial situation will soon improve noticeably. If the spider moves away from the person, it means major expenses are ahead.
• If a spider climbs onto a person, then a high income awaits him.
• A cobweb that appears in a car will certainly bring happiness. The spider acts as the protector of everyone who rides on it.

Purpose of the limbs

The functions of spider limbs are varied. They are used to weave, level and secure the web, the females place the young on their backs, and hold the cocoon of eggs on the body.

Other tasks are also being solved:

• movement in space;
• blocking production;
• touch;
• determining the location of the sound source;
• soil research;
• digging holes

Spiders use their strong front legs to fight their opponents, delivering crushing blows. If this does not lead to a positive result, powerful chelicerae are used - a kind of claw-like jaws. Many predators have spine-like processes on the segments of their legs, with the help of which they comb and straighten the tangled web.