Do pit-building predators prefer or avoid barriers? Wormlions preference for walls depends on light conditions

摘要

( ) Photos of wormlion pits in an urban habitat (Tel Aviv University, photographed by IS). Wormlion pits are often constructed adjacent to building walls. ( – ) Schemes of the experimental designs. We used arenas of 15 × 15 cm for all experiments. Wormlions were always placed individually in each arena. ( ) Experiment 1: wormlions were placed either in shallow sand (0.5 cm depth; left) or deep sand (2 cm depth; right), either in the arena centre (dashed arrow) or next to the arena wall (continuous arrow). Experiment 3 was designed similarly to Experiment 1, but instead of a sand-depth treatment with two levels, we either exposed arenas to full light or covered them to induce full shade. ( ) Experiment 2: The arena included a stripe of deep sand (rectangular grey area) surrounded by shallow sand. Wormlions were placed either in deep sand (left) or shallow sand (right). They were either placed next to the wall (continuous arrow) or in the arena centre (dashed arrow). Experiment 4 was designed similarly to Experiment 2, but instead of a sand-depth treatment, we used a rectangular-shaped cover providing full shade (the grey area) surrounded by full exposure to light in the rest of the arena. ( ) The follow-up experiment comprised two treatments: the arena was fully exposed to light or one of its walls provided a 3-cm stripe of shade. Wormlions were individually placed 3 cm from the wall (arrows).