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Key words. Wormlion, antlion, Vermileo, Euroleon, substrate particle size, sand, powder
Abstract. Wormlion larvae are found in substrates consisting of fine sand or powder, implying that they may be able to distinguish between different substrates according to particle size. To estimate the effects of particle size on wormlions, the pit-building decision of the larvae of the wormlion Vermileo vermileo was observed in four substrates consisting of different sand fractions. Wormlion larvae prefer the finest sand fraction with particle size ≤ 230 µm. When wormlions (Vermileo vermileo) and antlions (Euroleon nostras) are placed in the same container with two different substrates, interspecific predation does not occur. In two-substrate choice tests larvae of the two species show opposite preferences for two substrates offered. While wormlion larvae readily build pits in the finest sand fraction (≤ 230 µm), antlion larvae prefer coarser sand (with particle size 230-540 µm). Wormlion preference for the finest sands and powders, and antlion preference for sands of medium particle size was confirmed by field observations. Sand particle size affects the spatial distribution of sand-dwelling insect larvae and thus may reduce conflicts between heterospecifics.
INTRODUCTION
Wormlions (Diptera: Vermileonidae) are of great interest to biologists. It is the only dipteran family known whose larvae capture prey by constructing pits in loose soil (Wheeler, 1930; Ludwig et al., 1996, 2001). Larvae of antlions (Neuroptera: Myrmeleontidae) similarly use funnel-shaped pits to capture prey. In contrast to wormlions their predatory behaviour is extensively studied. Only a few antlion species build pitfall traps, and this is considered to be the most specialized strategy for capturing prey within the Myrmeleontidae (Gepp & Hölzel, 1989; Mansell, 1996, 1999). Pit-building antlions wait at the bottom of the pit for prey. The antlions are generally located at the pit centre but may move away from the centre over time (Fertin & Casas, 2006). They feed on small arthropods that slide into the pit. The antlion larva detects its prey from a distance of a few centimetres by sensing the vibrations that the prey generates during locomotion (Devetak et al., 2007; Mencinger-Vra..ko & Devetak, 2008).
The antlion pit both funnels prey to the jaws of the larvae (Lucas, 1982) and retards the escape of the prey (Griffiths, 1980; Devetak, 2005). When the prey...