Substrate Choice in Antlion Larvae: the Combined Effect of Particle Size and Moisture

Abstract The choice of substrate in sedentary predators is influenced by abiotic factors that impact foraging efficiency and survival. We examined the combined effects of substrate particle size and moisture on microhabitat selection and pit-building behaviour in two antlion species: Myrmeleon formicarius and Euroleon nostras . Both species strongly preferred medium particle sizes (G2, 230–540 μm). When the preferred substrate was moistened, the larvae of both species switched to one that was coarser, but dry (G3, 540–1000 μm), prioritizing dry conditions over optimal particle size. However, when we moistened both G2 and G3, the larvae displayed flexibility in their behavioural responses. While E. nostras primarily moved to the finer substrate (G1, 110–230 μm), M. formicarius was evenly distributed between dry G1 and G3, which had residual moisture. The preference shown by M. formicarius could be attributed to its broader tolerance for precipitation since it inhabits exposed environments with larger particle sizes compared to E. nostras . Pit diameter generally correlated with substrate granulation, but we did observe differences between the species. E. nostras constructed larger pits in the preferred substrate despite having a smaller body size. In contrast, M. formicarius built larger pits in coarser substrate. This suggests that pit-building strategies appear to be influenced by multiple factors, including substrate, larval morphology, and behavioural plasticity. G4 (>1540 μm) was unsuitable for both species. These findings highlight the interactive effects of particle size and moisture on habitat choice and demonstrate how microhabitat constraints influence the behaviour and life strategies of trap-building predators.