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Species: Nymphister kronaueri beetle

Habitat: Army ant abdomens and nests in rainforests of Costa Rica

Moving around the rainforest floor can be tough if you’re tiny. But a newly discovered species of beetle has an ingenious method of getting around with little effort: it bites on to an army ant’s butt and hitches a ride.

Nymphister kronaueri uses its mandibles to do this when its hosts are on the move to a new nest, attaching between the ant’s thorax and abdomen.

This emerged after Christoph von Beeren at the Technical University of Darmstadt in Germany and Daniel Kronauer at the Rockefeller University in New York noticed that an ant they were observing in a collection vial looked as though it had two abdomens.

“When Daniel shook the vial, the beetle detached and expanded its legs and antennae. That is the moment we realised we had discovered something new here,” says von Beeren.

Army ants frequently move to new colonies, so the beetle would be left searching for a new host colony almost every night if it didn’t have some way to keep up, he says.

Free taxi

Hitching rides with army ants in this way is nothing new. Other critters regularly ride on their backs, follow in their wake on foot, or stow themselves on top of “booty” that the ants carry from nest to nest. N. kronaueri’s method of clinging on as a second rear end appears to be unique, however.

The army ants, which assume the role of an unwitting rainforest taxi service, might have a hard time noticing that N. kronaueri is there: the beetle has cunning adaptations to look like its host’s abdomen, being similar in both size and appearance.

It may seem strange that the ant wouldn’t notice a beetle hanging from its rear, and precisely how the creature fools both its host and others in the colony is still unknown.

What exactly N. kronaueri gains from all this deception is not well understood either, because information about its basic biology has yet to be collected.

But other hitchhiking species exploit ant colonies for protection from predators, to find a place to sleep, and so they can get food easily without having to look too hard themselves.

Joseph Parker at Columbia University in New York says that when looking at adaptations in species that live with and depend on ants, the “bizarre almost becomes the norm”. But among those, he says, N. kronaueri’s adaptation is one of the most remarkable.

Given that N. kronaueri managed to go undetected by people, despite living with one of the most well-studied species of army ant��(Eciton mexicanum), von Beeren suggests it’s highly likely there are more of these bizarre critters out there waiting to be found.

Parker agrees, adding that the strategic use of ants by other species is an underexplored area of biology: “This is evolution at its most extreme: the more we look, the more these creatures force us to modify our ideas of how organisms make a living.”

Journal reference: BMC Zoology, DOI:

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