Pit‐relocation of antlion larvae in relation to their density

Abstract

SummaryOf the biotic factors potentially affecting the foraging behavior of pit‐building antlion larvae, Myrmeleon boreTjeder, we focussed on the density effects and examined experimentally influences of larval density on pit construction behavior, spatial distribution and pit relocation rate. Moreover the mechanism of mutual interference among larvae was examined. After releasing 2, 5, 10, 15, 20 and 30 third instar larvae of M. bore at the center of each container (30×30×10 cm3) filled with sand, we measured number of pits, pit diameter and position of pit base. More than 80% of antlion larvae at each density always constructed pits, and the rates of larvae that had not constructed pits rose in proportion to the density. Pit size was approximately constant independent of the density. The density of M. bore larvae clearly affected the residence time of the pits, i.e. more larvae frequently relocate pits with increasing larval density. To analyze the spatial distribution pattern of the larvae in a container, nearest neighbor distance (NND) was measured. Comparison between the observed NND and the expected value for NND in random distribution obtained from computer simulation suggested that high larval density produced a uniform distribution owing to their mutual interference. The result of an experiment to examine the mechanism of mutual interference among larvae showed that frequent dropping of sand into a pit tossed by neighbor antlion larvae causes a pit‐relocation.