Factors determining the prey size of the orb-web spider, Argiope amoena (L. Koch) (Argiopidae)

Argiope amoena is a common web spider in southwestern Japan. Surveys were made of prey size by use of prey traps and by direct observations, and of potential prey size by use of the sweeping method. The web size, web mesh size, spider size, and spider's effective size on prey capture were also measured. Hymenoptera, Coleoptera, and Hemiptera were important as prey for female A. amoena which is far larger than male. Small insects such as dipterans, which are numerous in the surrounding vegetation, were excluded as prey of the female. It seems that small insects pass through the web mesh. A. amoena caught prey nearly twice its own length. The upper limit of prey size coincided with the distance between the first and third legs of A. amoena; these legs are used for prey handling and silk-wrapping. It seems that large insects above the upper limit escape by defeating the spider or by breaking the web.