Why are flying insects entangled in the web, and not the spider itself, which moves freely along it?

Probably, you often see in cellars, basements or in nature a stretched web, which contains insects that are eaten by a spider. The spider itself easily moves along its trapping net from one victim to another. It would seem that the limbs of all arthropods, which include both spiders and insects, are arranged in the same way. But only “guests” stick. Why is this happening?

From ancient times

For the answer, let’s turn to the evolution of spiders. The very first spiders appeared in the Silurian period (about 440 million years ago) and lived in the sea. They came from small arachnids, aquatic arachnids.
Initially, the spider web was used as a way to attach to the bottom in shallow water, so that the wave would not be carried away into the open ocean. In addition, shelters were woven from the web, at first very simple – the gap between the two stones was woven with a thread, and this became a kind of “tent” for the spider.
With the arrival on land, spider web construction took on a new evolutionary round. Not only dwellings and safety threads were woven from it, but also cocoons for eggs.

Trapped victim
However, back to the spider houses. Most of them were attached to the landscape with stretched threads. When a victim passed by, the spider detected it by the vibrations of the thread.
Over time, there were two main directions in the evolution of spiders:

some hunted small invertebrates or set up ambushes,
others began to improve trapping nets.
The first spider web was found in amber 100 million years old.

Sticky nets

Since then, there have been many innovations in the evolution of spiders. One of them is a sticky spider web covered with small droplets of sticky liquid. The victim is easily confused.
So why doesn’t the spider get entangled in it – the answer is simple – the spider weaves non-sticky threads into the web for its movement. Knowing the web by heart, he easily moves along it and simply bypasses dangerous zones. Insects, on the other hand, get entangled in the spaced nets because, having touched the sticky string, the victim begins to beat, in attempts to peel off, and therefore touches even more threads until it is completely entangled. The owner knows from the hesitation of his snare that someone has come for dinner. Then the spider can only inject digestive juice into the victim’s body and suck in the half-digested “broth” from the insect.