Contrasting patch choice behaviour by immature ambush predators, a spider (Misumena vatia) and an insect (Phymata americana)

1. Spiderlings of the crab spider Misumena vatia and nymphs of the ambush b ug Phymata americana normally ambush prey in flowers, as do the adults. The immatures of M. vatia are more mobile, by ballooning, than the ambulatory but largely sedentary adult female spiders, but the apterous immatures of P . americana are less mobile than the alate adults. The aim of the work repo rted here was to investigate how immatures, as compared with adults, select sites from which to ambush their prey. 2. Individual immatures of both species were released in experimental arena s with variously manipulated natural stems: normal, with and without leaves , and with and without flowers of three species of plants. 3. The spiderlings and nymphs showed discriminatory behaviour but not in ac cordance with optimal foraging in either case. The spiderlings chose more l eafy stems than any other kind of stem. For the nymphs, the importance of l eaves was less marked, food apparently being more important than shelter. 4. Neither of the predators discriminated among flowering stems of Solidago canadensis, Daucus carota, and Cirsium arvense. 5. In other experiments, in which flowered and deflowered stems were locate d in two separated,groups in the arena and the individual was released in a bare area between the two groups, the spiderlings chose either group as pr edicted by chance but the nymphs showed a slight preference for the flowere d sector. Nevertheless, once in either of the groups, the predators showed similar behaviour in choosing leafy stems more often than other stems. 6. Nymphs of P. americana are much more selective than adults but spiderlin gs of M. vatia are less selective than adult females. These results appear to accord with the time and energy costs of changing hunting sites, walking being slower than flying or ballooning. 7. The results indicate the need to include other parameters, such as enemy -free space and time spent in not being able to forage, in the analysis of foraging behaviour.