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This study tests hypotheses regarding spider cocoons and their suspension systems as barriers to generalist and specialist predators. Evidence presented here suggests that the suspension systems ofMecynogea lemniscata andArgiope aurantia cocoons are effective barriers against small generalists such as ants, but fail to stop large generalists such as birds. Cocoon covers were found to be generally ineffective against generalist predators. Various component layers of these cocoons are shown, however, to be an effective barrier against the attack modes of specific predator guilds. Cocoon covers function primarily as barriers to specialists that use active "burrowing" larvae to gain entrance into the cocoon, while the flocculent silk layer is shown to be an effective barrier against specialists which use a long ovipositor to attack cocoons. These findings support suggestions that the primary role of the cocoon is to provide protection from predators and parasites. These results also support a close evolutionary relationship between cocoon architecture and specialized predators.

The abilities of the cocoons of the spiders Mecynogea lemniscata and Argiope aurantia to protect the enclosed egg and spiderling stages from desiccation were investigated in the laboratory under controlled humidities, and in the field under ambient conditions. For M. lemniscata, which has a relatively small clutch (8-30 eggs) and remains in the cocoon for approximately 9-10 months, removal of the cocoon had no effect on water loss from the egg stage, nor did it adversely affect hatching or molting success. Cocoon removal did, however, significantly affect water loss and, consequently, survival in the spiderling stage at all humidities in the laboratory and in the field. The importance of the cocoon for survival is probably related to the unusually long time M. lemniscata spiderlings spend in the cocoon overwintering. For A. aurantia, which has a substantially larger clutch size (300-1400 eggs) and remains in the cocoon for a shorter 6-7 months, cocoon removal had no effect on water loss, egg hatching success, molting success, nor spiderling survival. The lack of an effect suggests that other factors (e.g., relative humidity at the oviposition site, or a large clutch size) may be more important in controlling water loss for A. aurantia.