On Being a Caterpillar: Structure, Function, Ecology, and Behavior

Abstract

In nearly all terrestrial biomes, and especially those dominated by woody plants, caterpillars make up much of the above-ground insect biomass, playing central roles as herbivores, prey for higher trophic levels, and nutrient cyclers. Likewise, they hold special status as the most ecologically conspicuous and taxonomically diverse clade of insect herbivores, with global species diversity likely in excess of 300,000 species. Much of this richness stems from the fine-grained nature of their host plant associations—more than 85% of lepidopterans are believed to be dietary specialists that consume one or a set of closely related host plants. We draw attention to two key attributes of caterpillars that have additionally contributed to their evolutionary success: their collective set of predator avoidance stratagems and manifold and novel uses of silk to solve ecological problems. A principal goal of this introductory chapter is to provide information to ecologists and others about the structure, function, and life history of caterpillars: their basic external and internal anatomy, larval development, population biology and ecology as consumers and the consumed, and other salient attributes. In addition to highlighting many of their adaptations, we make mention of some of their morphological and evolutionary limitations and draw attention to many matters about their biology that remain unexplored or unanswered. We also share much new caterpillar life history data for North American moths.

Last instar Eupackardia calleta (Saturniidae). When alarmed the caterpillar secretes clear droplets rich in biogenic amines from its dorsal scoli, here from segments A3 and A7–A9; the droplets repel ants and other invertebrate enemies. Photo by Mike Thomas