The feeding strategy of a crab spider, Diaea sp. indet. (Araneae: Thomisidae): post‐capture decision rules

Post‐capture decision rules and the mechanisms and constraints controlling these rules were examined in a New Zealand crab spider, Diaea sp. indet. Diaea envenomates prey, principally in the head and thorax, and injects the total amount of venom it uses to immobilize prey within 15 s of the prey being captured. Diaea injects a larger volume of venom into larger prey, which demonstrates that this species can regulate the amount of venom injected. Diaea usually feeds from two sites on the prey—initially the head, then the posterior abdomen. Prey envenomated in the thorax or abdomen are re‐oriented by the spider so it can begin feeding from the prey's head. During feeding the exoskeleton of the prey remains intact. Diaea initially mixes digestive fluid, secreted from itsmidgut, with the contents of the prey. Fluid is then extracted from the prey using suction provided by the combined action of pharyngeal muscles and a sucking stomach. The sucking phase of feeding generates a pressure deficit (vacuum) within the prey and alternates with a relaxing phase, during which the spider stops sucking and the extracted fluid flows back into the prey. Both the sucking and relaxing phases lengthen as increasing volumes of fluid move between the spider and the prey. Reflux of fluid into the prey allows Diaea to mix digestive fluid with parts of the prey that are not in the immediate vicinity of the spider's mouthparts. Fluid is refluxed at an increasing distance from the spider's mouth as the lengthening sucking phase increases the vacuum within the prey.