How voracious antlions engineer deadly sand traps

You’d never know it by looking at the dragonflylike adult antlion, but its wingless larvae—fingernail-size eating machines with huge, poison-filled jaws—build deadly sand traps to capture tiny insects, including ants. Now, scientists know precisely how they do it: As the hapless prey falls into its pit, an antlion at the bottom uses its head to fling a blizzard of sand grains up the funnel-shaped slope, creating a minilandslide that pulls the unfortunate insect to its doom. The pits, scientists say, are feats of engineering—and physics.

To figure out how the larvae create such effective pitfalls, German scientists used high-speed videography to watch lab-reared antlions ensnare ants and small crickets in small, sand-filled terrariums (see video, above). The researchers then dug their own artificial sand traps and saw that the prey was able to escape out of the pit when a larva wasn’t inside flinging up sand.

Comparing decades-old biological observations with engineering models, the researchers found that by hurling sand grains, the antlions constantly maintain the pit’s “angle of repose”—the steepest possible angle before the sandy slope starts to slide. The sand storms not only discombobulate prey, but they also maintain the geometry of the sand traps and ensure the antlions don’t get buried themselves, the team reports in a preprint on bioRxiv.

The new study reveals antlion larvae must constantly maintain their traps to keep them in working order—and to catch enough prey to last the 1 to 3 years before they transform into graceful, less deadly adults.