The caterpillars of the Sphingidae family, known widely as hawk moths, sphinx moths, or hornworms, are defined by their remarkable size and voracious appetites. This larval stage is dedicated almost entirely to consuming foliage to fuel the rapid growth necessary for metamorphosis. The volume of plant matter these large larvae consume often makes their dietary habits a significant concern for gardeners and agriculturalists. Understanding their specific food sources reveals a fascinating story of insect-plant co-evolution and biochemical specialization.
Identifying the Hawk Moth Caterpillar
Hawk moth caterpillars possess a distinct appearance that makes them relatively easy to identify in the garden. They are typically large, reaching lengths of up to four inches, with stout, smooth bodies that often display colors optimized for camouflage, such as bright green or brown. The most defining feature is the prominent, fleshy structure known as the caudal spine or “horn,” which is found near the tail end on the eighth abdominal segment. This harmless projection is the reason many species are commonly called hornworms. In North America, the two most frequently encountered species are the green Tomato Hornworm (Manduca quinquemaculata) and the similar Tobacco Hornworm (Manduca sexta), alongside the more generalist White-lined Sphinx (Hyles lineata).
The Primary Host Plants
The diet of most hawk moth caterpillars is highly specialized, often centered on a single family of plants. For many of the most recognizable species, the primary food source belongs to the Solanaceae family, commonly known as the nightshades. This plant family includes many commercially grown crops, such as tomato, potato, eggplant, and pepper, all of which are frequently defoliated by the Tomato and Tobacco Hornworms. Tobacco plants also fall within this group, serving as the dedicated host for the Tobacco Hornworm, which is uniquely adapted to its specific chemical composition.
Beyond the nightshades, other hawk moth species target distinct plant groups. The Achemon Sphinx caterpillar (Eumorpha achemon) feeds on plants within the grape family, such as cultivated grapevines and Virginia creeper. The White-lined Sphinx is a more generalist feeder, consuming plants like evening primrose, purslane, and various species of dock. Other species, such as the Great Ash Sphinx (Sphinx chersis), depend on the foliage of trees and shrubs, including ash, lilac, and olive-family plants.
Feeding Habits and Dietary Specificity
Hawk moth caterpillars are characterized by their rapid, high-volume intake of plant material. The larval stage is focused entirely on storing energy for the non-feeding pupal and adult stages, requiring accelerated growth. A mature hornworm can consume up to four times its own weight in plant matter daily, often leading to the quick defoliation of host plants over its two to three-week feeding period.
The ability of these caterpillars to consume toxic plants, particularly nicotine-rich nightshades, is due to specialized biochemistry that allows them to metabolize these compounds. For example, the Tobacco Hornworm processes nicotine from its host plant and releases it through its spiracles, using the toxin as a defensive chemical deterrent against predators. This dietary specialization, known as oligophagy, ensures the caterpillar receives a consistent, high-quality food source while reducing competition. The adult moths, in stark contrast, are exclusive nectar feeders, relying on their long proboscis to sip from deep-throated flowers.