Factors Confronting a Shelter-Building Caterpillar at Spring Emergence

Abstract

Weather often subjects overwintering small invertebrates to heavy losses and forces survivors emerging from the litter to respond quickly to achieve short-term success. On spring emergence both feeding and predator avoidance may compete for immediate attention. Caterpillars of the shelter-building fern moth Herpetogramma theseusalis suffer high mortality while overwintering in the litter, and survivors often emerge in parlous condition, thus facing urgent pressure both to feed and to seek protection, since they experience predation and parasitism as well. Accordingly, I addressed whether they prioritized feeding or shelter-building upon emergence. Caterpillars built shelters during the night of their emergence, and many remained in these shelters for five days or more, though a minority soon abandoned their initial sites, presumably to build a subsequent shelter. If I removed their shelter, caterpillars built replacements before feeding, even though losing 10% or more of their mass in the process. Some completed up to five shelters following repeated removals, losing up to half of their mass, including several that died. Subsequently-built shelters declined to as little as one-third their original volume. Thus, they prioritized shelter production over feeding, notwithstanding the high cost in lost growth and time. In contrast, caterpillars not building shelters gained 37–44% in mass/day. Although some of these manipulations exceeded the normal experience, they illustrate the strength of selection favoring protection.