Assassin bugs cover themselves in sticky plant resin to trap prey

In a rare instance of insect use of tools, a bug enhances its hunting success by bumping itself into the sticky resin of grass.

Australian assassin bug from the genus goraedubius, spinifex are often seen resting on blades of grass. A feature of Australia’s arid regions, this grass produces a sticky resin that was very popular with Australia’s first human inhabitants for making tools.

Biologists have suspected that some species of triatomine bugs may be using spinifex resin to capture prey, but this has never been tested experimentally.

His fellow Macquarie University colleague Marie Herberstein collected 26 assassin bugs in the Kimberley region of Western Australia and brought them to a laboratory in an open-air tent.

They noticed that males, females, and immature nymphs scraped the resin off the spinifex leaves and meticulously applied it to their bodies, especially their forelimbs.

Each worm was placed in a glass jar and two preys, a housefly and an ant, were offered one at a time. Next, the researchers removed the resin from the bug’s body with a makeup remover pad and repeated the experiment.

Insects were 26% more successful at capturing prey when equipped with resin than when not equipped. Without resin, flies were 64% more likely to escape.

The resin didn’t guarantee success, but it did appear to slow the prey just enough for the assassin bug to grab and sting.

Soley and Herberstein say this is a definitive example of tool use by a very rare insect. This behavior seems to be hard-wired into bugs, and even newly hatched and orphaned nymphs have been found coating themselves with resin.

Christiane Weirauch of the University of California, Riverside said: “It’s like insects camouflaging themselves with debris and dead ants.”

Using tools is often thought of as a sign of high intelligence, but that’s not always the case, says Weirauch. “I would argue that tool use is not only genetically fixed, but may have a learning component. Getting closer to animals, animals such as primates and octopuses incorporate more learning into tool use.”