By Emily Harwitz
You would never know by looking at the dragonfly adult ant lion, but its wingless larvae – fingernail-sized eating machines with huge, poison-filled jaws – build deadly sand traps to catch small insects, including ants. Now scientists know exactly how to do it: As the unfortunate prey falls into its well, an ant lion at the bottom uses its head to throw a snowstorm of grains of sand up the funnel-shaped slope, creating a mini-island shift that the unfortunate insect takes to its demise. The wells, scientists say, are engineering feats – and physics.
To find out how the larvae create such effective traps, German scientists used high-speed videography to look at lab-grown antlions trapping ants and tiny crickets in tiny, sand-filled terrariums (see video above). The researchers then dug their own artificial sand traps and saw that the prey could escape the pit if there was no larva inside that splashed sand.
By comparing decades-old biological observations with engineering models, the researchers found that by swinging grains of sand, the antions constantly maintain the pit’s “angle of rest” – the steepest possible angle before the sand slope begins to slide. The sandstorms not only disrupt the prey, but they also maintain the geometry of the sand catchers and ensure that the antlions themselves are not buried, the team reports in a pre-print bioRxiv.
The new study shows that ant lion larvae must constantly maintain their traps to keep them in good condition – and to catch enough prey for 1 to 3 years before turning into graceful, less lethal adults.