Some 20 species of spiders have evolved a social life that is distinguished by exceptional cooperation among the known 50,000 species of spiders. One or two of them hunt 'in a pack' with the others. Anelosimus eximius, a tiny arachnid found in French Guiana, has colonies that can house several thousand individuals of all ages in enormous webs that can reach several cubic meters in volume. This little red spider's behavior is quite surprising when prey such as a moth or grasshopper falls into their web. They immediately begin to attack in unison, pausing only when necessary. That way, they can detect vibrations from their prey, which can be several hundred times their size, and time their arrival with the arrival of their hunting party.

It was recently discovered by a team from the Center de Recherches sur la Cognition Animale (CNRS/Université Toulouse III - Paul Sabatier) what mechanisms are involved in this type of collective hunting. The actions that were involved in the timing of these movements were identified by the researchers. They publish a description of them in the journal PNAS.

The scientists studied the hunting habits of two feral colonies in French Guiana to learn more about their behavior. They attached a miniature motor to the webs and adjusted the pattern and intensity of the vibrations to simulate the movements of an insect that had been captured. To observe the behavior of the spiders, the authors placed vibrating lures on their webs, which the spiders responded to. They discovered that the spiders moved in a synchronous manner, without the presence of a leader. Each of them is aware of the vibrations produced by its companions and ceases to move as soon as they threaten to drown out the movement of the prey. Once their own vibrations have subsided, the spiders begin to move again in their webs. They accomplish this by subduing their prey as quickly as possible.