Warrick Angus
Habitat use and feeding ecology of the redback spider, Latrodectus hasselti
B.Sc.(Hons) 1999
Understanding habitat use by animals is of particular importance when establishing
patterns of distribution. In the case of sedentary animals, the habitat used
may have concentrated influences on an animal's life history and fitness. The
redback spider (Latrodectus hasselti) is a classic sit and wait predator, which
lives a fundamentally sedentary life.
I conducted a field survey in several sites throughout the Sydney region to identify abiotic and biotic parameters that may influence the success of the redback spiders. In particular, I examined the associations of aspect, conspecific density, substrate type, temperature, web size, abundance of prey assemblages and prey captured with respect to juvenile, intermediate and adult redbacks. All redback spider development stages had a non-random use of habitat with respect to substrate. Manipulation of substrate types in a laboratory experiment demonstrated that redbacks appear to select stable hard substrates for web construction over less stable substrates.
Analysis of prey items from webs in the field suggested that adult redbacks are euryphagous predators capable of catching prey considerably larger than themselves. Conversely, juvenile redbacks appear to be stenophagous with a smaller range of prey captured. Morphological comparisons between juvenile and adult redbacks found spinneret structures were considerably variable, corresponding to different web structure and strength between developmental stages. The cost of web construction was measured in mass lost for juvenile spiders and was found to be of considerable importance to a hatchling spider. Ants (Hymenoptera: Formicidae) were the most abundant prey item for all spiders, however, juvenile redbacks reared on this diet in a laboratory based experiment performed least well in comparison to cricket (Acheta domestica) or mealworm (Tenebrio molitor) diets. Survivorship, growth and development for juvenile redback spiders is likely to be influenced by a number of parameters, such as substrate, prey availability, and web efficiency. These findings suggest there is a benefit to juvenile redbacks to select sites that provide least disturbance to webs as well as being placed in a suitable prey rich environment.