Effect of substrate density on behaviour of antlion larvae (Neuroptera: Myrmeleontidae)

Sand-dwelling antlion larvae are well known predators with a highly specialized prey-catching strategy, which either construct efficient pitfall traps or bury themselves in the sand ambushing prey on the surface. Although habitat selection in antlions has been extensively studied, little is known about the role substrate density plays in such behavioural decisions. We thus first quantified the natural substrate densities of 13 antlion species by collecting soil samples from 18 different field sites. We found that natural substrate densities varied from 121 g/l to 1562 g/l. The substrate densities of three non-pit-building species (Neuroleon microstenus, Distoleon tetragrammicus, Nophis teillardi) ranged from medium to high, while those of obligatory pit-builders (Euroleon nostras and eight Myrmeleon species) were more variable. The substrate density of the facultative pit-builder Cueta sp. was high. Next, we explored the responses of the pit-building antlion E. nostras to different substrate densities using both a habitat choice and a complementary no-choice experiment. We hypothesized that antlions should be capable of distinguishing between substrate types and that pit size should decrease with increased substrate density. When allowed to choose among eight substrate densities, E. nostras larvae preferred to build their pits in the fractions with low densities (i.e., 121, 353 and 512 g/l) and only a small proportion constructed pits in high density fractions (i.e., 1312 and 1546 g/l). A complementary no-choice experiment demonstrated that pit diameter, pit depth and pit angle were negatively correlated with substrate density. These reductions in pit size can negatively affect prey capture success.

► Substrate densities in natural habitats of 13 antlion species originating from four continents are presented.
► We examined effect of substrate density on pit-building decision and pit size in antlions.
► Pit diameter, pit depth and pit angle are negatively correlated with substrate density, which affect capture success.