The discerning predator: decision rules underlying prey classification by a mosquito-eating jumping spider

Abstract

Evarcha culicivora is an East African jumping spider that feeds indirectly on vertebrate blood by choosing blood-fed female Anopheles mosquitoes as prey. Previous studies have shown that this predator can identify its preferred prey even when restricted to using only visual cues. Here, we used lures and virtual mosquitoes to investigate the optical cues underlying this predator's prey-choice behaviour. We made lures by dissecting and then reconstructing dead mosquitoes, combining the head plus thorax with different abdomens. Depending on the experiment, lures were either moving or motionless. Findings from the lure experiments suggested that, for E. culicivora, seeing a blood-fed female mosquito's abdomen on a lure was a necessary, but not sufficient, cue by which preferred prey was identified, as cues from the abdomen needed to be paired with cues from the head and thorax of a mosquito. Conversely, when abdomens were not visible or were identical, spiders based their decisions on the appearance of the head plus thorax of mosquitoes, choosing prey with female characteristics. Findings from a subsequent experiment using animated 3D virtual mosquitoes suggest that it is specifically the mosquito's antennae that influence E. culicivora's prey-choice decisions. Our results show that E. culicivora uses a complex process for prey classification.

Fig. 1.

Equipment used for prey-choice testing. (A) Testing arena for motionless-lure tests. The apparatus consisted of a glass arena (square box, 100×100 mm, walls 35 mm high), with a removable glass lid. Holes in the box connected with four ‘choice’ vials flanked by lures. Lures in position ‘a’ are different from lures in position ‘b’. (B) Testing apparatus for moving-lure tests. A 35 mm deep rectangular glass box (pale grey) with a glass lid sat on top of a wooden stand (grey). Moving lures were controlled through a camera release-cord. The ‘choice area’ is the dark grey semicircular area within wire circles. (C) Apparatus for virtual-prey testing. Images pass from a data projector lens through a second lens (for reducing image size) onto a stimulus screen positioned in front of the higher end of the ramp.

Fig. 2.

Linear regression of the size of corneal lenses of the principal eyes of Evarcha culicivora in relation to carapace width. Eyes were measured using an ocular micrometer to the nearest 25 μm (N=977 spiders).