Add a little-known species of assassin bugs to the list of animals that can fashion and wield tools. And true to their name, the insects use that tool to draw their prey into an ambush, researchers report May 12 in Proceedings of the National Academy of Sciences.
Found in Thailand and China, Pahabengkakia piliceps is a species of predatory insects called assassin bugs that has a taste for the region’s stingless bees. When researchers at Xishuangbanna Tropical Botanical Garden in China began studying the assassin bugs in 2021, they became intrigued by how P. piliceps hunt. While lying in wait at a hive’s entrance, the assassin bugs use their front legs to proficiently pick off bees that fly by.
Recordings of them in the wild revealed that before getting into position at the hive entrance, P. piliceps apply a sticky resin on their front legs. Worker bees leave this resin on the hive’s exterior to trap and attack intruders like ants or spiders, but the assassin bugs use the sticky stuff against the bees.
Lab experiments revealed assassin bugs break up dried blobs of resin at the hive entrance, releasing a bouquet of chemicals into the air. Tricked by the smell, worker bees may mistake the waiting predator for a trapped intruder and go straight toward its outstretched front legs, the researchers say.
Multiple species of assassin bug are well-known tool users. They use sticky plant material to trap their prey, but P. pilliceps go a step further. “They’re not using the resin as it is.… They’re manipulating it,” says Fernando Soley, a behavioral ecologist at the Western Australia Museum in Welshpool who wasn’t part of the study.
Compared with cognitively demanding forms of tool use like those found in humans, chimps and crows, this is much simpler. “They have the impulse to put resin on their front legs” even when bees are not around, says Li Tian, coauthor of the study and an entomologist at China Agricultural University in Beijing. This indicates that the behavior is a basic biological instinct, rather than an action performed with intention. It’s like being born with a skill without knowing what it’s for, says Soley.
More complex ways of shaping and using tools likely evolved by polishing innate tendencies. Studying rudimentary tool usage in insects could help us understand how sophisticated tool usage evolved in animals like humans.
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