Prey Capture

Many insecticides are known to either excite or depress insect feeding, with differences seen among species and instars of the same species (Haynes 1988). Data collected in our laboratory suggests that prey capture by spiders is affected by sublethal doses of malathion. Both orb-weaving spiders and irregular web spiders appear to stop prey capture completely. Hunting spiders (R. rabida and S. scenicus) also show both a significant reduction in prey capture and in feeding on captured prey. Salticus scenicus is used here as an example of the test procedure. Prior to testing, spiders were fed one vestigial-winged Drosophila melanogaster then removed from food access for 7 days. Animals were then exposed to 10 ul of 10 ^-4 malathion or water. Following a 12-hr exposure, their behavior was recorded using a video camera suspended above the test arena. We remained out of their view and watched behaviors on a monitor (salticids have excellent vision and respond to the investigator's movements; Crain 1949). A fly was released into the arena and the spider's behavior was recorded for 10 min. Dosed spiders showed a 20% decrease in prey capture as well as several other behavioral disturbances. Dosed animals more often over- or undershoot their prey when capturing, failed to maintain their hold when prey were captured, more often avoided prey, and bumped into prey without capturing. We have also recorded improper visual tracking of prey not seen in the control animals (example below)

Normal Traking of Prey

The above image shows the normal tracking response of S. scenicus to prey. As the prey enters the visual field of the anterior lateral eyes (analogous to our peripheral vision; shown in yellow in the cartoon), the spider turns to lock on with the anterior median eyes (analogous to our foveal vision; shown in green on the diagram). The spider then follows the prey using the anterior median eyes.

Abnormal Prey Tracking.

The second animation shows improper tracking seen by dosed animals. Spides improperly lock on using the anterior lateral eyes (shown in red) and never turn to view the prey with the anterior median eyes. While normal animals usually attacked the prey after locking on with the anterior median eyes, dosed animals that tracked with the anterior laterals never approached the prey. Although not all dosed animals exhibited this type of tracking, none of the undosed spiders showed improper prey tracking.