Silk stealing by Argyrodes lanyuensis (Araneae: Theridiidae): a unique form of kleptoparasitism.

In this study we used field surveys and experiments to investigate silk stealing, a unique form of kleptoparasitism. We studied the role that silk stealing plays in the interactions between a kleptoparasitic spider Argyrodes lanyuensis and its giant wood spider host Nephila maculata by testing: (1) if silk stealing generates any cost to the hosts; (2) if the amount of web lost to kleptoparasites varies with the size of the host; and (3) how prey stealing by A. lanyuensis affects N. maculata. Compared with uninvaded webs, N. maculata webs invaded by A. lanyuensis suffered an average orb reduction of 21%. There was a significant negative correlation between the percentage web reduction and body length of N. maculata, indicating that the impact of silk stealing was greater on younger hosts. No significant correlation was found between the number of A. lanyuensis on orbs and orb loss, but there was a significant negative relationship between percentage orb loss and silk diameter of N. maculata. These results suggest that the finer silk of smaller hosts may be at least partially responsible for their higher percentage orb loss. While prey stealing by other Argyrodes species greatly affects the foraging gain of hosts, A. lanyuensis did not seem to affect N. maculata. This was because the host took larger prey than the kleptoparasite did, and less than 3% of the host's biomass intake came from prey that A. lanyuensis would steal. Copyright 1998 The Association for the Study of Animal Behaviour.