We believe them to be solitary, alone weaving their web on our ceilings or in the depths of our gardens. But the spiders are not all isolated. Young, they are all more or less social and gregarious, before dispersing. Only regarding twenty species, out of the 50,000 known, continue to have a social life.
Present in the tropics, they have a very sophisticated collective organization, which goes from the manufacture of the silky trap on sometimes several cubic meters, to hunting in packs which allows them to catch prey up to 700 times larger than ‘she. And we now know, thanks to a team of Toulouse researchers, how they manage to coordinate to swoop down on their prey simultaneously.
No leader, but vibes
They observed these colonies of Anelosimus, small orange spiders that do not exceed 7 to 8 mm present in Guyana. During their attacks, when an insect becomes entangled in their web, they alternate phases of movement, then simultaneous stopping. A little as if they were playing “Jacques said”. Except that none of them is there to give an order to the others.
They will modulate their movement in unison according to the vibrations emitted by the prey, but also their congeners. “They will remain motionless on the web as long as the vibrations emitted by the other spiders mask those of their prey, then resume their attack and swoop down on their prey, which they bite at the same time. They therefore modulate their behavior, which allows the colony to be flexible in its reactions to prey”, explains Raphaël Jeanson, member of the Toulouse Animal Cognition Research Center (CNRS/UPS) and co-author of a study on the subject published this week in the specialized scientific journal PNAS.
And in function, to also know according to the vibrations emitted, if it is necessary a battalion of 60 or 500 spiders to overcome their meal of the day. They will also cooperate with each other when it comes to building the trap or pulling their prey into a spot. Less loved than ants, these little invertebrates are no less fascinating.