Unlike most spiders, which weave their homes with silk threads in high areas, crabs prefer to build their refuges in burrows under rocks or next to tree trunks. “They can dig their own holes or take advantage of existing ones in the soil”, says biologist Antônio Domingos Brescovit, from the Butantan Institute, in São Paulo. Generally, burrows are proportional to the size of the animal and are not usually very deep. A nocturnal animal, the crab – the popular name given to several species of spider with a large and hairy body – is found in gardens, forests and thickets of grass. In some countries it is known as a tarantula. A peculiarity of these spiders is the fact that they only have two pairs of spinnerets (the structures used to weave threads), while most spiders have three pairs. They usually live isolated and feed on small cold-blooded animals, such as reptiles and amphibians, insects and even small birds. With the chelicerae, two small claws located near the head, they pierce and inject venom into their prey and eventual aggressors. All are poisonous, although those existing in Brazil have a venom that is not very active in humans. Crabs of the genus Atrax, found in Australia, are among those that can kill a person.
1 – The crabs build their refuge under rocks, next to fallen logs or in shallow holes. They prefer nests close to the ground, because, due to their size – the largest reach 30 centimeters! —they would be too exposed in webs. Close to the ground, they are also more likely to find food.
2 – To dig the burrows, they use a kind of small tooth located in front of the chelicerae, name given to the claws they use to sting their prey. These little teeth, also called rake, are a series of adapted hairs, similar to a brush with metal bristles.
3 – After digging the hole, it is necessary to remove the earth. When it comes to cleaning the house, the crabs throw the rubble backwards with the help of their front legs, pushing the dirt out of their nests.
4 – The finishing work is meticulous: some crab plants line the hole with silk threads. This coating has several functions: keeping the place clean, preventing the entry of ants and serving as a warning — when an animal bumps into the web, the spider immediately detects the intruder, as the thread is an extension of its sensory system.