Abstract

1. The effects of density, feeding regime, and body size on interference competition in the pit-digging larvae of the ant-lion Macroleon quinquemaculatus (Hagen) were investigated in laboratory experiments. 2. Competition had little effect on the pit size of winners but losers constructed much smaller pits than isolated larvae. Losers were less likely to dig or maintain pits and more likely to move than winners. 3. Competition was much stronger between well-fed larvae than between hungry ones, and well-fed competitors showed reduced growth rates. Well-fed larvae orientated themselves so that they could throw sand into their neighbour's pit whereas hungry larvae faced away from each other. Differences in hunger level reversed the competitive advantage of larger larvae only when individuals were of similar size. 4. Cannibalism was density-dependent and most frequent in hungry, similar-sized, larvae; the smaller larva was usually the victim. 5. Displays/challenges between larvae affected the distance between pits. Body size was the main determinant of contest outcome though pit ownership and hunger level also had an effect.