Antlion larvae follow optimality rules in body orientation during sand-tossing

Pit-building antlion larvae (Myrmeleon spp.) throw sand at prey that approach their pit using their head and mandibles as a backward-directed ‘biological catapult’. This mechanism restricts effective sand tossing to a defined angular range behind the larva. When prey-like vibrations come from outside this range, antlions are known to reorient, but the consistency and rules behind this behaviour remain unclear. We tested whether larvae follow optimal turning strategies when reorienting toward a vibrating stimulus placed in disadvantageous positions along the pit. Across 128 trials (19 individuals), larvae responded in 45 trials (∼35%). In responding trials, initial orientation strongly predicted turning direction: larvae rotated along the shortest angular path to reach the optimal sand-throwing orientation. These results provide evidence that antlion reorientation towards the prey is non-random and follows a minimisation rule, revealing a previously unnoticed behaviour.