Colony survivorship of social caterpillars in the field: a case study of the small eggar moth (Lepidoptera: Lasiocampidae)

Abstract

We investigated survivorship of 100 caterpillar colonies of the tent-building central place-foraging moth, Eriogaster lanestris. Our aim was to demonstrate if survival patterns match those reported for the related eastern tent caterpillar, Malacosoma americanum, which has a similar social system. The field experiment took place at four sites in northern Bavaria, Germany, in May and June 2002. Egg clusters were obtained from females mated in the laboratory and were exposed in the field just before hatching of the young caterpillars. Establishment of larval tents and survivorship on the colony level was then monitored until completion of larval development. In total, 52% of colonies had at least one larva surviving until pupation, with no significant differences between the four study sites. Colony-level mortality rate was constant over time and did not drop markedly during the last two larval instars, when E. lanestris larvae develop urticating hairs that are presumed to confer protection against vertebrate predators. The inability to build an initial tent, or the later loss of the tent, accounted for 71% of the observed total colony losses. Strong rainfall had a severe influence on the constitution of tents and increased the likelihood of colony failure. Overall, maintenance of an intact tent emerged as the single most important predictor of colony survival.