Foraging Specialization in Orb‐Weaving Spiders

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Previous studies indicate prey—specific attack behaviors in orb—weaving spiders. This study explored functional relationships between the morphology of contrasting orb—weaver species and their prey—specific attack capabilities. Araneus trifolium and Argiope trifasciata were observed attacking acridid Orthoptera, calyptrate Diptera, and Lepidoptera in the laboratory. Diets and habitat use of spiders in the field were determined by surveys. Distributions of prey types were determined by trapping. Araneus captured Orthoptera more quickly than did Argiope, but Argiope was more successful in capturing this prey type. There were no attack time differences between spider species on dipterans and lepidopterans, but Araneus captured these types more successfully. Attack times do not appear to limit prey intake rates in the field. Spider morphology and web design appear to interact in causing the above behavioral differences. Araneus builds its web in high, open sites, usually in herbaceous vegetation. Argiope tends to build its web in low sites in both grassy and herbaceous vegetation. Prey distributions are such that each spider species is found most often in sites where its more successfully captured prey type is relatively more abundant. Predation and physiological stress may also select for these differences in habitat use. If these results are extended to other species, the following predictions arise. Spiders with relatively short, stout legs, large fangs, and high, simple, open—meshed webs (such as Araneus) should specialize on innocuous, rapidly escaping prey types (Diptera and Lepidoptera). Spiders with relatively long legs, small fangs, and low, densely meshed, ornamented webs (such as Argiope) should specialize on dangerous, slowly escaping insects (Orthoptera, Homoptera, Hymenoptera).