Within the 50,000 known species of spiders about 20 have developed a permanent social life characterized by a remarkable cooperation. Among these, one or two species hunt "in packs," such as the Anelosimus eximius spiders of French Guyana, whose colonies can house several thousand individuals of all ages, coexisting peacefully in gigantic webs that often reach several cubic meters. When prey falls into their web, the spiders instantly adopt astonishing behavior: Synchronizing their attack by coordinating phases of moving and stopping, they strike as one. In this way, they are able to capture prey up to several hundred times their size.