Predatory characteristics of ant-eating Zodarion spiders (Araneae: Zodariidae): Potential biological control agents

Some ant species are important nuisance pests. Mechanical and chemical strategies are currently used to control them. Biological control, based on the use of a natural enemy, has not yet been proposed. The aim of this study was to investigate the predatory efficiency of ant-eating Zodarion spiders as possible biological control agents of ants. The investigation included identification of prey specificity, study of the functional response, and the consumption rate. Two species were used, Zodarion rubidum and Zodarion styliferum. Z. rubidum was found to be a Formicinae specialist as it was more efficient in the paralysis of Lasius and Formica ants (both Formicinae) than in the paralysis of Monomorium, Tetramorium, and Messor ants (all Myrmicinae). The functional response of Z. rubidum was Type II in the small arena and Type IV in the large arena. Although spiders killed up to 24 ants during 12 h, only a few prey items were actually consumed. The overkilling thus amounted to 80-100% and was due to specialized predatory behavior, in which ants are consumed some time after being immobilized. Spiders usually started to feed only if no living ant was around. Juvenile spiders of Z. rubidum consumed at most two Lasius ants consecutively, the handling time being prolonged with the later prey captured. During 26 days juveniles of Z. styliferum captured 21 ants, but their exploitation of ant biomass decreased with time. It is concluded that Zodarion spiders possess some features typical of biological control agents, however, further experiments are necessary to assess their real potential.