Did you know that spiders belong to the phylum known as anthropods? Most people believe spiders to be insects but they are not. They are one among the four classifications of anthropods known as arachnids. The other three include the myriapods, crustaceans, and insects.
In the arachnid family there are spiders, scorpions, ticks and mites. Spiders are not the only arachnids with eight legs. Scorpions and other arachnids also have four pairs of legs as well.
Spider legs total eight in number and these creatures can still get around and survive even when they lose a limb. Spiders have more legs than they need according to scientists. They came to this conclusion following studies on spiders caught in the wild that were missing one or two legs. These spiders were still able to reproduce, build similar webs to their eight legged counterparts and hunt just as effectively.
Having said that spiders can’t afford to lose too many legs. In fact, two seems to be the limit as those with fewer legs did not survive out in the wild. They built less structured webs and their hunting game was off. They also couldn’t escape predators fast enough.
When a spider loses its legs it does so at the predetermined break point which is typically close to the body itself. The breakpoints have the natural ability to clamp shut to prevent he spider from bleeding out due to loss of a lim. They have a special muscle group that facilitates the clamp down. The process of voluntarily losing a limb is called autonomy.
Spiders have the ability to regrow back that leg in time as long as is loss doesn’t hamper their ability to hunt and move around. That is why losing more than one limb becomes dangerous for spiders in the wild.
How do spider legs work?
Because spiders are mainly terrestrial creatures they get to move along the ground most of the time. They use their legs to move around but also to secure their prey when hunting. When using its legs the spider employs the use of its muscles as well as its circulatory system. Spider blood, also known as hemolymph, is pumped into the legs making them expand outwards and facilitate movement. To move them back inwards the spider’s muscles contracts them pushing the hemolymph back into the body’s cavity.
This natural ebb and flow of hemolymph is crucial for movement which is why when the spider loses a limb it quickly clamps the affected joint to prevent too much blood loss. And the hydraulic movement doesn’t have the aid of flexor and extensor muscles that insects and other limbed creatures have.
With regard to their skitter from side to side they instinctively decrease or increase their body pressure to jut out some hemolymph to the limbs every few fractions of a second to achieve this movement. Apart from powering their movements, the expulsion of the spider blood from the cavity combined with the hydraulics, powers their genitalia for mating.