Frequency, composition and variation in external food stores constructed by orb-web spiders

Few examples of food hoarding have been documented in spiders, yet two Australian species of orb-web spiders, Nephila edulis and N. plumipes, typically incorporate previously captured prey into the web. The effect of prey density and prey-encounter rate on the storage behaviour of adult female N. edulis was tested in the laboratory. Prey density had a significant effect on the propensity to construct external caches: when more food was available, food caches were larger than when the supply of prey was limited. Caching behaviour also differed with the rate of prey encounter, even though the total amount of food supplied was the same. When prey were encountered at constant rates, spiders allocated more food to external storage compared with random encounter rates. Finally, we tested the quality of different prey types for external or internal storage. N. edulis were fed with blow-flies or crickets, and these prey were stored in the web, discarded or totally consumed. Crickets were typically consumed or stored, while flies were more frequently discarded. Field observations of the storage behaviour in N. edulis and N. plumipes found surprising differences in the composition of the cache. While N. plumipes incorporated only animal material, N. edulis also utilised plant material, suggesting that the storage band in N. edulis has other, non-food-storing functions. Field experiments indicated that the presence or absence of external stores in the web of N. plumipes had no influence on mortality, weight gain, or the presence of Argyrodes kleptoparasites.