Spiders extend their legs out by utilizing the increase in blood pressure induced by their heartbeat.

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Have you ever cleaned your floor and spotted a small dead spider nestled among the dust bunnies? Perhaps if you looked closely, you noticed its short legs tucked up tightly against its torso.

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Spiders lack the muscles necessary to stretch their legs, resulting in this spidery leg-curl of death. Rather than that, they harness the power of fluids! Spider legs are composed of a series of tubes.

The “hip,” or the joint where these tubes link to the body, functions similarly to what you might expect. It has extensor muscles that are used to extend the legs and flexor muscles that are used to curl them in. 

On the other hand, the remaining joints on spiders’ legs include just flexor muscles. 

According to some scientists, relying on hydraulics arose as a result of the fact that removing extensor muscles makes room for larger, more powerful flexor muscles. Spiders employ their flexors’ curling-in motion to grasp their prey and climb the basement walls. As a result, they are able to completely exploit their flexing abilities because they do not need to engage extensors.

Spiders may even propel themselves through the air using their unique leg construction. To begin, they contract their flexor muscles and inflate their leg joints. Then they rapidly release them, and the near-instant extension drives them upward.

However, when a spider dies, it exhibits all of the typical indications of death, including rigor mortis. When the muscles of a corpse flex, the body becomes stiff. 

There is a lot going on at the molecular level here, but the critical point to remember is that muscle relaxation requires ATP. Due to the fact that a dead body produces no ATP, the muscles rapidly deplete it and become caught in clench mode until they disintegrate sufficiently to end rigor mortis.

Being dead also means that a spider’s hemolymph is no longer compressed. As a result, those legs are free to flex, which is why they are always curled. If the thought of spiders caught in the traditional death stance makes you sad, the following may cheer you up:.

Spiders’ hydraulic legs are so astonishing that some scientists are exploiting them to create powerful yet lightweight and flexible robots. 

Summary

The blood pressure of the house spider Tegenaria atrica was measured inside its leg. Pressures of around 5 cm. Hg have been found, as well as transitory pressures of up to 40 cm. Hg.

A relationship has been discovered between leg blood pressure and extension torque at the hinge joints.

When accelerating a load anchored to the leg, significant torques can be produced at the hinge joints during extension. These torques can be explained by the transitory pressures that occur in the leg.

There is a discussion of the hydraulic mechanism. According to the research, the pressure seen in the legs also occurs in the prosoma but not in the belly, implying that the heart is responsible for the maintained pressure. This, on the other hand, necessitates additional examination.

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