How a trap-jaw ant carries a baby

Outsized mouthparts aren’t just weapons

Odontomachus brunneus ant

Powerful jaws make the Odontomachus brunneus ant a skilled escape artist.

Alex Wild 

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Surprisingly gently. That’s how Odontomachus ants use their trap jaws to move soft, wriggly larvae around the nest. When ants hunt, though, those same jaws can smack shut at speeds exceeding 200 kilometers an hour.

“The poor prey are smashed. Sometimes they stick to the teeth; sometimes they bounce away,” says Fredrick Larabee of the University of Illinois at Urbana-Champaign.

The difference between butcher and nursemaid is in the ant’s preparation. Before a killing strike, jaw muscles clench hard. Their pull distorts parts of the head that will pop back into shape, powering the jaw to slam the instant a trigger muscle frees a latch. For slower, gentler tasks, the ants use jaw muscles with the latch unlocked.

The O. brunneus ant, at more than half a centimeter long, looms as a hulk among all trap-jaw species. Lock-and-spring-load jaws evolved at least four times independently in ants, but mostly among tiny species. Miniature ants use trap jaws to hunt equally tiny springtails, which use their own springs to fling themselves airborne and escape attack. The trap jaw versus springing tail represents “an evolutionary arms race in terms of speed,” Larabee says.

Just what pushed the evolution of trap jaws in ants as big as O. brunneus remains a puzzle. They don’t specialize in springtail nuggets, but trap jaws might help with other fast — or dangerous — prey. Larabee says that Odontomachus ants are known to kill termite soldiers that shoot a noxious defensive chemical out of their heads.

Power-amplified jaws could even improve the ants’ chances of surviving some of their own predators, Larabee and Andrew Suarez report May 13 in PLOS ONE. They let O. brunneus trap-jaw ants skid down the sandy sides of traps dug by a predatory insect called an ant lion (SN: 7/12/14, p. 4). The ants doubled their survival rate if they were free to fire their jaws against the ground and recoiled skyward.

“In real life it happens so quick — you blink, you miss it,” Larabee says. It’s almost more fun to watch on YouTube. Almost.

 A trap-jaw ant can use its mandibles to make a rocketlike emergency exit from a hidden killer’s pit.

F.J. Larabee and A.V. Suarez/PLOS ONE 2015

Susan Milius is the life sciences writer, covering organismal biology and evolution, and has a special passion for plants, fungi and invertebrates. She studied biology and English literature.

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