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The threads are produced in a gland located in the animal’s abdomen. Depending on the species of spider, these threads are used to form different structures and designs, which also vary depending on the purpose of the construction. The main types of webs are used for capture, copulation or refuge (see the text below), but there are also webs for molting, which are used by some species that change their external skeleton. Two well-known spiders produce very characteristic webs. The black widow makes a completely irregular design, which has nothing to do with the geometric precision of some constructions. Some crabs have the habit of preparing a very dense web on the ground, where they can hide. “It is usually the females who build the webs. Males only do this occasionally,” says biologist Irene Knysak, from the Butantan Institute, in São Paulo. Silk threads are extremely resistant and elastic.
With a thickness equivalent to one-tenth of a human hair, they can be stretched, without breaking, 40% beyond their normal length – twice the elasticity of nylon. Experts calculate that a thread of web as thick as a pencil would even be able to stop a Boeing 747 in mid-flight!
Glands produce the threads, which are adjusted in thickness by special hairs
1. In the abdomen of spiders there are some glands called serigen glands. They secrete a type of protein in a liquid state
2. This substance leaves the spider’s body through a kind of tiny tubes, the spinnerets. Located at the back of the abdomen, they control the amount of webbing expelled.
3. When the liquid protein comes into contact with air, it becomes a fine silk thread, with which the web will be built. At the ends of the spinnerets there are several hairs that look like small claws and serve to adjust the thickness of the yarn produced.
Delicate constructions can have several purposes
capture web
It is the one we see the most and serves to trap small insects that will later be devoured. Part of it is covered in a slimy substance, which sticks to victims.
copulation web
As the name implies, it serves as a nuptial nest for spiders. It has the shape of a small cup, in which the male deposits the sperm to later place it in the female.
web of refuge
It is the spider’s own home. It is formed by a large tangle of threads, usually taking the form of a small tube.