Ozaena are by no means the first beetles to take advantage of ants. A distantly-related group—Paussus beetles—have actually achieved a small degree of infamy for this behavior. Paussus beetles are the Trojan horses of the insect world: After conning their way into ant nests, female Paussus will lay eggs that hatch into sweet-smelling larvae, thought to exude an irresistible bouquet of ant attractants. Lured in by the scent, ants approach—only to be punctured and sucked dry by the ravenous, vampiric larvae. Paussus adolescents thus spend their early days gorging on an essentially unlimited, self-sustaining supply of protein-rich food.

When beetles invade ant nests, they initiate “an exploitative relationship,” says Brittany Owens, an entomologist at the Louisiana State University Agricultural Center who was not involved in the study. “The ants really get a bum deal.”

And from the beetle’s perspective, it’s a pretty cushy lifestyle compared to, say, the toils of burrow trapping. “If you are able to socially integrate inside ant colonies and gain acceptance inside nests, you have no predators,” says Joseph Parker, an entomologist who studies beetle-ant relationships at the California Institute of Technology who was not involved in the study. “There are infinite resources for you to feed on. You’re in a really safe, stable environment. The payoff is really big.”

Receive emails about upcoming NOVA programs and related content, as well as featured reporting about current events through a science lens.

So there’s a big motivation to make the switch from burrow to nest. But beetles can’t just integrate into ant society willy-nilly. The change requires some substantial evolutionary rejiggering: Ozaena’s ancestors, which gave rise to burrow trappers, likely split off from the Paussus line at least 100 million years ago. This means Ozaena had to find its own way ant-ward—a feat that required these beetles to shed millions of years of adaptations that had tailored their relatives to burrows, and instead take on traits that would allow them to raid unfamiliar nests, lay their eggs in the presence of strangers, and meet their nutritional needs with only one source of food.

The shift is so difficult and so extreme that it’s only happened a few times in beetles, Moore says. And if Ozaena beetles have indeed traded their lineage’s long history of burrow trapping for a life of juice-guzzling luxury, they would be the only members of their subfamily that parasitizes ants in the United States—making them the ant-munching black sheep of the family.

“I’m always amazed by the adaptations that these insects show,” Parker says. “Your jaw hitting the floor is the standard response.”

Ozaena beetle larvae (top) lack many of the specialized structures that their close relatives in the Goniatropus genus (bottom) use for their burrow trapping lifestyle, including a disc-like appendage at their rear ends that helps the larvae sense when prey passes over their burrow. Image Credit: Wendy Moore, University of Arizona

Despite their similarities, though, Ozaena isn’t simply a Paussus copycat—and in their time apart, Ozaena has come up with its own strategies to make the most out of nests. For instance, while Paussus larvae are pretty much immobile blobs that must wait for their meals to come waddling by, the Ozaena specimen boasted unusually long legs that might have helped it scurry around the nest to actively hunt its prey.

“When we think about beetles, we only think about adults,” Moore says. “But larvae aren’t just big bags of goo. They represent this entire hidden world.”

Besides, “it’s the most vulnerable stage,” Moore says of the larvae. “If they don’t make it, the species doesn’t make it.”

Share this article

Major funding for NOVA is provided by the David H. Koch Fund for Science, the NOVA Science Trust, the Corporation for Public Broadcasting, and PBS viewers.