Adaptations for Locomotion at Low Body Temperatures in Eastern Tent Caterpillars,Malacosoma americanum

Abstract

Locomotor performance of spontaneously foraging tent caterpillars (Malacosoma americanum) was videotaped under various thermal conditions as growing colonies progressed from the third through the sixth larval instars. Stride length and, therefore, speed increased with increasing body size. Speed and stride frequency were strongly temperature-dependent ($Q_{10}$ of 2.2 and 1.9), whereas stride length was less affected by temperature ($R_{10}$ of 1.2). Tent caterpillars showed little convergence between temperature preferences and thermal physiology; most of their foraging activity occurs at temperatures that greatly reduce locomotor performance. The absolute slowness of caterpillar locomotion appears to have favored an activity pattern in M. americanum that is based on temporal avoidance of predators. The absence of predators during nocturnal foraging has apparently resulted in little selective pressure for a thermal physiology, which promotes relatively rapid locomotion at low body temperatures.