How many legs does a spider have, or Why is it not related to insects?

The oldest arachnids that now live on Earth are scorpions. Millions of years have passed, and they have not changed much. Today, science knows more than 700 of their types.

Scorpios - the inhabitants of not only desertlocalities, as is commonly believed. They are also found in humid and hot tropics and subtropics, some species can be found in cooler places - in the mountains at high altitudes above sea level. But ticks are a relatively young group of spider-like arthropods. But in my article I will give preference not ticksand scorpions, namely spiders, even though I don’t particularly like them. It is interesting to trace how the evolution and reduction of the external structure of the spider, caused by the merging of the segments and distinguishing it from the scorpion, took place in the process of evolution. Here I will answer the perennial controversial question about how many legs a spider has, and I will also tell you what its web is made of. Go!

What does he look like

The external structure of the spider is also fundamentallydistinguishes it from insects. If their body clearly consists of three sections: the head, thoracic and abdominal, then the arachnids of these departments are only two: the cephalothorax, formed by the merger of the head and chest and consisting of durable chitin, and a soft belly. There are already eight eyes on the head of the head! Do not be surprised, but generally the minimum number of spider eyes is six, the maximum is twelve.

The cephalothora is connected with a soft belly with a very thin and small tube. At the end of the non-segmented abdomen are the so-called spider warts. I will tell you about their purpose below.

How many legs does a spider have?

Many of us still can not properlyanswer the question of how many legs a spider has and probably think that there are six of them, like all insects. But it was not there! This is the main difference - the presence of precisely eight legs, while insects, in fact, have only three pairs of legs. The first pair of spider legs are chelicerae. These are poisonous head limbs, which are used to trap and crush food. Next come three pairs of legs designed for walking.

Here we are with you and we know how many legs a spider has, fromwhat departments it consists of, how many pairs of eyes it has and, perhaps, the most important thing is that it is not an insect! These are its main external features. We turn to the internal "spider review."

The internal structure of the spider

This is the brain-controlled nervous system,located in the cephalothorax. The spider also has a heart, which is located in the upper front part of the soft abdomen (red in the figure). The frequency of the heartbeat is 30-70 beats per minute, but if the spider is strained or exhausted for any reason, this frequency increases to ... 200 beats per minute! At the end of the abdomen are the so-called spinning organs. They produce silk and are associated with glands that produce various proteins. As a result of mixing and polymerization of proteins, thin silk is produced, which passes through special spinning organs and turns into a thread. Here it is - the web!

Habitat

Spiders are spread absolutely all over the world -from Antarctica and highlands to deep gorges and caves. Many of them live on land, and some - in the seas, in freshwater sources and in groundwater.