Small, but powerful: The behavior of a tiny spider, which biologists have now uncovered through high-speed recordings, looks like martial arts from a fantasy film. The hunting technique consists of an acrobatic sling attack, in which a silk thread is fastened to the perplexed victim in a flash. Then the robber dances around her prey and wraps it up so that she can safely attack the death bite. As the researchers point out, the "ant-slayer" achieves with its concept what other spiders are usually unable to do: it overpowers defensive ants.
Some lurk in holes, some lunge at their prey, and others weave elaborate webs: the world's thousands of spider species have evolved numerous techniques and strategies to capture insects. However, they do not pounce on everything that crawls into their field of vision or kicks in the web: In order not to take unnecessary risks, spiders usually avoid defensive insect species. In this way, ants in particular were able to keep the robbers at bay. Many ant species are heavily armed with powerful biters and often venomous stingers. They can quickly become the last prey of a daring spider. Although ants are so numerous, only very few species of spiders target the rabid crawlers.
How does the "Ant-Slayer" defeat her dangerous prey?
With one particularly striking exception, the biologists around Alfonso Aceves-Aparicio from Macquarie University in Sydney have now looked more closely. Australian orb spider Euryopis umbilicata forages on the trunks of eucalyptus trees at dusk. It was already known that these arachnids, which are about one centimeter in size, also prey on ants. This has earned the species the name "Ant-Slayer". However, it was unclear exactly how they manage to do this, because their prey capture takes place in fractions of a second and is therefore not visible to humans with the naked eye.
First, the team investigated which prey the spider is targeting. “Amazingly, almost all of the prey consisted exclusively of Camponotus consobrinus ants. Such extreme prey specialization as in this spider is unusual as they typically feed on different prey types,” says Aceves-Aparicio. "Moreover, most predators attack victims that are smaller than themselves. But in this case, the ants are about twice the size of the spiders," the biologist points out. Aceves-Aparicio and his colleagues then used detailed behavioral analyzes to discover how they overpowered the well-fortified giants. To do this, they collected C. consobrinus ants and released them individually in front of the spiders. The team filmed what happened next at up to 250 frames per second.
Whirling Blitz hunting technique
The analyzes of 60 hunting sequences showed that hunting takes place in phases. First, the spider performs an acrobatic lightning attack: In just 300 milliseconds, it hurls itself onto the ant with a twisting motion, attaching a sticky spider thread from its abdomen to it and the surface. The anchored victim is then tied up: the spider circles the ant at a safe distance in order to wrap more and more spider silk around it. She then bites the defenseless victim to finish him off. Dangling from a silk thread, the robber then drags her prey to a quiet spot to eat. "The acrobatic, very rapid immobilization and subsequent wrapping of the prey with silk apparently enabled these spiders to tap into this abundant but dangerous prey as a food source," Aceves-Aparicio concludes.
Any ants that were successfully tied to the trunk with the silk during the initial acrobatic fall were killed, the researchers found. According to them, it is characterized by an extraordinarily high success rate in catching prey. The ant-slayer spiders far outperform known rates of ant-hunting insect species, as well as other apex predators: cheetahs, and lions and wolves that hunt in groups, are typically successful in less than 50 percent of their hunting maneuvers, the researchers write.
Source: University of Hamburg, specialist article: PNAS, doi: 10.1073/pnas.2205942119
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