In Australia, assassin bugs use a deadly tool to capture snacks: the resin of the spinifex grass. Recent research shows that creeping creatures cover themselves with sticky gum to catch and hold their prey.

Although unusual, some insects use tools, from ants, which use particles to build bridges, to baby insects, which use excrement as a parasite deterrent. Previous reports of assassin bugs collecting plant resins indicate that this species uses tools more often than others.

This makes assassin bugs “a particularly promising case for understanding the ecological and behavioral conditions that facilitated the otherwise unlikely evolution of tool use,” the authors say.

Because tool use requires a certain level of sophisticated cognition, this was once thought to be a way to distinguish humans from other animals, but researchers are now finding more examples of tool use in the animal kingdom.

Before our thumbs fully developed dexterity, humans used tools, and it turns out that not even the earliest tools were made by humans. Dolphins protect their beaks with sea sponges, pigs with sticks, and even savvy birds and bees come into play.

The scientists assumed that the assassin bugs’ hunting success would increase if they were coated with sticky plant resin, but this was not tested in the experiments.

Macquarie University biologists Fernando Soli and Marie Herberstein observed 125 Australian assassin bugs from the unidentified species Gorareduvius from the Kimberley region of Western Australia, in the wild and in a makeshift laboratory in a nearby tent.

Australian assassin bugs appear on the trunks of Triodia, a native bushweed commonly known as spinifex. It is found in the arid regions of Australia and produces a sticky resin prized for its use by the early Australians for making hunting gear.

Soli and Herberstein speculated that if resin was used as a tool, resin-coated insects would be better at catching prey than non-resin-coated insects. They took 26 assassin bugs found near or on the curly rose (Triodia bitextura) back to their glamorous tent labs for research.

The researchers placed the beetles in a glass jar with a stick and introduced two types of prey: flies and ants. They then carefully wiped the resin from the insects’ bodies using make-up removal pads and repeated the experiment.

Insects tended to be more successful at catching ants than flies, and more importantly, they were more effective at catching prey when they had resin in their bodies, regardless of the type of prey.

The tar-covered insects were 26 percent more successful at catching all types of prey than their unarmed counterparts. Flies are difficult to catch even on a good day, and 64 percent of the flies Horareduvius came into contact with survived without resin.

The researchers observed that both in the wild and in the lab, Horareduvius scraped resin from spinifex leaves and carefully applied it to their bodies, particularly their front legs. Even newly hatched and isolated nymphs were found to be covered in resin, suggesting that this behavior was caused by insects.

According to the authors, this corresponds to commonly used definitions of tool use.

“Assassin bugs manipulated an environmental object (resin) by removing it from its usual context and applying it to their bodies,” they write, “gaining a selective advantage through improved prey capture.”

The term “assassination bug” brings together a variety of insects combined with their gruesome way of killing their prey. As a rule, the predator pierces the prey with its proboscis, injecting digestive enzymes into it that paralyze and kill it, and then pull the liquid contents from the victim, leaving an empty shell.

“Prey never fully adhered to the resinous surface of assassin bugs,” Soli and Herberstein explain. “In contrast, the prey’s short-term, transient adhesion, delayed response seems sufficient for assassin bugs to catch and sting their prey.”

So, while resin isn’t a guarantee of success, it’s a tool that slows down this Australian beetle’s prey enough for the assassin bug to catch and kill it. The study was published in Biology Letters.