Decisions better left unchanged: Selection of ambush orientation before prey arrival in a sit‐and‐wait predator

Abstract Modifying decisions depends on the cost of change, especially in sit‐and‐wait predators. Once situated, and before prey arrival, they should remain immobile because any changes in their position inside the pit can disturb their traps or alert prey and predators. Antlion larvae ( Myrmeleon spp.) dig conical pits in the soil to capture walking arthropods, often ants. The larva then ejects the prey carcass using its mandible as a catapult. Therefore, its orientation in the pit determines the direction of expelling debris. We tested the hypothesis that antlion larvae orient themselves at the bottom of their pits to avoid future movements and that they decide their position based on environmental features such as the proximity of vertical obstacles and the ground's slope. In the field, we dropped standardized debris into pits located near and far from walls and recorded the direction of their expulsion. The expelled debris direction was consistent as larvae maintained their position at the bottom of their pit throughout time, and their position was independent of the pit's distance from a wall. In the lab, we induced larvae to build pits in narrow and sloped terraria. Larvae oriented themselves to avoid expelling objects towards a wall or uphill, preventing them from bouncing off or rolling back into the pit. These results suggest that during trap‐building, larvae use environmental information to decide how to position themselves at the bottom of the pit to avoid posterior movements. Our findings emphasize the importance of gathering accurate environmental data to avoid position shifts before prey arrival, which can reduce the capture efficiency of sit‐and‐wait predators.