We know that lions, for example, hunt in packs. But what about spiders?
Some species of spiders that live in groups of thousands in huge webs, synchronize their movements to catch insects much larger than themselves. Now we know how.
Of the 50,000 known species of spiders, the vast majority become solitary in their adult form and there are barely twenty social species, but only one or two hunt in groups (they are only gregarious during the early stages of their development), but when they do, they are lethal. When insects dramatically fall into their web (pun intended), the spiders synchronize their attack, moving like a single huge spider to catch animals up to 700 times heavier than an individual arachnid.
How do they decide their attacks?
Although some species of spiders are known to hunt in packs, exactly how they do so has been a mystery to scientists. Until now.
To better understand this fearsome form of arachnid attack, a team of researchers led by Raphaël Jeanson of the University of Toulouse, France, altered the webs of two colonies of Anelosimus eximius , a species of social spider whose females range in size from 4, 4 to 6 mm, while males are probably even smaller.
After creating this modeling , they mimicked the movement of the prey with a dead fly connected to a vibration generator in contact with a web , creating vibrations in different parts of the webs, while filming the spiders’ movements.
“Nests are typically composed of a horizontal, basket-shaped silk sheet and a network of vertical threads, connected to vegetation, used to intercept flying prey,” the researchers say.
What happened to the artificial lure?
Their observations revealed that pack hunting among these spiders was not directed by a primary arachnid leader, but rather that all spiders “hear” what is happening in other parts of the web and react accordingly by synchronizing and coordinating their movements. According to the researchers, the arachnids only stayed still long enough to distinguish the vibrations caused by their fellow spiders from those of their prey.
“Depending on the size of the prey, and the vibrations that the prey creates in the web, the spiders must be more or less still to locate the prey without being disturbed by the vibrations of other spiders moving around,” comment the researchers. authors.
Thus, when one of them moves, they all start moving. This rule allows everyone to quickly adapt to any change.
Social spiders issue
Social spiders are noted for living together in large colonies (with gigantic webs that can reach several cubic meters), cooperating in capturing prey, sharing parental duties, and rarely straying far from their basket-shaped nests. A. eximius is one of those that cooperates permanently in the colony and is one of only two species that hunts ‘in packs’, helping them to catch insects, including moths, butterflies and grasshoppers that struggle to free themselves from the net. This social adaptation makes their menu exquisite, as no individual spider (of this size) could enjoy crickets or grasshoppers if she had to kill them alone.
Mind you, the more social spiders are, the smaller they tend to be, which means you’re unlikely to find giant spiders hunting in packs.
Referencia: Violette Chiara et al. A variable refractory period increases collective performance in noisy environments March 7, 2022 | 119 (12) e2115103119 | DOI: https://doi.org/10.1073/pnas.2115103119
