Zoological Studies

Vol. 39 No. 3, 2000

Argyrodes fissifrons Inhabiting Webs of Cyrtophora Hosts: Prey Size Distribution and Population Characteristics

I-Min Tso1,2 and Lucia Liu Severinghaus1,*

1Institute of Zoology, Academia Sinica, Taipei, Taiwan 115
2Department of Biology, Tunghai University, Taichung, Taiwan 407

I-Min Tso and Lucia Liu Severinghaus (2000) In this field study we in- vestigated the impact of Argyrodes fissifrons (Araneae: Theridiidae) on two species of Cyrtophora spider hosts (Araneae: Araneidae) by studying several aspects of its population and foraging. We examined (1) if natural population variations of A. fissifrons occur with different web sizes of the hosts, (2) if A. fissifrons form long-term associations with particular hosts, and (3) if the size range of prey consumed by A. fissifrons overlaps with that of Cyrtophora hosts. Results from field surveys indicated that a positive relationship exists between the average number of A. fissifrons and the size of the host webs. The number of A. fissifrons per host web per day changed daily, indicating the daily occurrence of immigration-emigration events. However, as inferred from monitoring marked A. fissifrons for 3 nights, some individuals form a long-term association with a particular host. The sex ratio, body size, and prey intake of A. fissifrons spiders staying in particular hosts' webs during monitoring did not differ from those that left a web. A significant difference was found in prey size distribution between Cyrtophora hosts and A. fissifrons, and the average prey size of the former was far greater than that of the latter. This result suggests that A. fissifrons scavenge on webs of Cyrtophora hosts by collecting small prey ignored by the hosts.

Key words: Argyrodes, Cyrtophora, Orchid Island, Spider.

*Correspondence: -