Spatiotemporal Variation in Antlion (Neuroptera: Myrmeleontidae) Density and Impacts on Ant (Hymenoptera: Formicidae) and Generalized Arthropod Foraging

Abstract Antlion larvae that construct conical pits to capture prey may strongly affect foraging of ants and other arthropods, yet are usually abundant only in sheltered microhabitats. Larval antlion (Myrmeleon crudelis Walker) densities increased in exposed areas in central Texas in late summer and early autumn of 1998, presumably because of extended dry conditions. I conducted a study to quantify larval antlion pit densities in sheltered and exposed areas over time, and to examine the effect of variation in pit density on the foraging activity of ants and other arthropods. Isolated rainfall events decreased pit densities in exposed areas, sometimes to zero, but pit densities returned to high levels as the soil dried out. Pitfall traps at sheltered sites caught significantly fewer ants and other arthropods inside antlion zones (i.e., areas of high antlion density) than in adjacent areas without antlions. At exposed sites, pitfall traps caught significantly fewer ants in antlion zones when pits were present (dry conditions) than when they were absent (wet conditions); there was no significant difference in foraging outside the antlion zones in wet compared with dry conditions. Significantly fewer ants were caught inside antlion zones at sheltered sites (that were permanent) compared with exposed sites (that were transient), although pit densities were similar at both types of sites. Attraction of ants to baits revealed similar patterns. Spatiotemporal variation in antlion pit densities and the associated predation risk to ants and other arthropods may result in behavioral modifications of foraging patterns, higher mortality rates, or both.

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