Animals

Oh, Snap! Trap-Jaw Ants Clamp Down on Prey in Half a Millisecond

Ants of the genus Myrmoteras have jaws that close at speeds up to 60 mph, and researchers now understand the mechanics of this evolutionary trait.

When your food moves fast, you’ve got to move faster.

For a type of southeast Asian ant, it helps that your jaw is spring-loaded to snap shut on prey in a tiny fraction of the time it takes a human to blink an eye.

The long, thin, spiny mandible of ants from the genus Myrmoteras open up at a 270-degree angle and lock into position, ready to snap shut when it moves on its most common prey — a jumping flea-like bug known as a springtail. When the ant is ready, a bulging spring of bone-like material at the back of the head releases the jaw, which snaps shut in half a millisecond — reaching speeds up to 60 mph in the process and spearing the springtail.

“Trap-jaw ants are likely evolving these really fast jaws for this specialized diet in sort of like an arms race,” said Fred Larabee, an evolutionary biologist at the Smithsonian Institution. “In order to capture their food, they have to have faster predation mechanisms than the prey they’re seeking out.”

Larabee, who works at the National Museum of Natural History in Washington DC, recently used high-powered imagery to capture the mechanism behind Myrmoterasmandibles for the first time.

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Fredrick Larabee, Smithsonian

The ants are native to Southeast Asia. The two Myrmoteras species in Larabee’s study were collected in Malaysia, where they live among leaf litter on the island of Borneo.

They’re one of several types of trap-jaw ants, some of which have more powerful jaws. But the mechanics of the ants in Larabee’s study were less well known. So he and his colleagues put the insects under a micro-CT scan and filmed them with a high-speed camera that captured 50,000 frames a second to reveal their movements.

“Their heads are very strangely shaped and they have this really prominent lobe on the back of the head,” he said. “While the mandibles are locked open, the closer muscle is able to supply tension to that spring in the back of the head.” When the jaw releases, “You can see that structure sort of caving in on the head. There’s a very clear deformation.”

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Larabee and his colleagues published their findings today in the Journal of Experimental Biology. The high-speed camera helped them pinpoint the speed of the jaws, while the CT scanner — which uses X-rays to produce a 3D image — “was really useful to look at the structures.”

“It’s a great tool for studying insect anatomy because you can resolve really small, delicate features of internal anatomy without having to break open the specimen,” Larabee said. “Being able to visualize that in a 3D environment is even more beneficial, because you can digitally dissect different parts and visualize just the pieces you’re really interested in.”

And it turns out trap-jaw ants have “completely different structures” to slam their mouths shut than other species.

“It’s a really great example of how evolution can come up with multiple solutions to the same problem,” he said.

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