Experimental Evidence that a Desert Parasitoid Keeps its Host Cool

The wasp parasitoid Pseudopompilus humboldti (Hymenoptera; Pompilidae) in the Negev desert of Israel stores its paralyzed host, the spider Stegodyphus lineatus (Araneae; Eresidae), at the entrance of the spider's nest. The spider is moved by the wasp from the depth of the nest to the entrance in spite of increased exposure to visually‐searching predators, such as birds. We examined the hypothesis that this behaviour has evolved to prevent the wasp's host from overheating in this hot desert. Experimental manipulations of the position of the parasitized spiders demonstrated that spiders and wasp larvae could not survive the heat experienced deep in the spider's nest during summer. By contrast, in the cooler nest entrance, spiders and larvae survived, if they were overlooked by predators. This host‐storing behaviour is an adaptive trade‐off between thermoregulatory requirements and predation risk. This appears to be the first evidence that a parasitoid manipulates the temperature of its host, albeit for its own ultimate gain.