The question of what a green caterpillar eats has a complex answer because “green” is a camouflage shared by thousands of species across the world. The color serves as a defense mechanism, allowing the larva to blend seamlessly with the foliage it inhabits, but it does not indicate a specific diet. What a caterpillar consumes is determined by its species, as each is genetically programmed to feed on a very narrow range of “host plants” that its mother chose.
Identifying Common Green Caterpillars and Their Host Plants
The diet of any caterpillar is rigidly species-specific. The larva will only consume the plant or group of plants on which its parent laid the egg. A caterpillar that hatches on a host plant is chemically and physiologically adapted to process the unique defensive compounds present in that specific vegetation. If moved to a plant that is not its designated food source, the caterpillar will starve.
Many green caterpillars are the larvae of common garden butterflies and moths. The bright green, smooth-skinned larvae of the Black Swallowtail butterfly, for example, feed exclusively on plants in the Apiaceae family, such as dill, parsley, fennel, and Queen Anne’s lace. Similarly, the green caterpillars of the Cabbage White butterfly, often called imported cabbageworms, consume plants in the Brassicaceae family, which includes cabbage, broccoli, kale, and cauliflower.
Another recognizable green larva is the Tomato Hornworm, which can grow to several inches long and sports a dark horn on its rear end. This caterpillar feeds on plants in the Solanaceae family, including tomato, potato, eggplant, and pepper plants, as well as related weeds like nightshade. The Luna moth caterpillar, a large, plump, lime-green species, is a generalist tree feeder, consuming leaves from a wider variety of deciduous trees, including birch, hickory, pecan, and sweetgum.
The Purpose of Continuous Eating
The sheer volume of food a caterpillar consumes relates directly to its goal: mass accumulation for transformation. A caterpillar’s growth is constrained by its non-elastic outer skin, or exoskeleton, which must be shed multiple times during its larval phase. These growth periods between molts are known as instars, and most caterpillars pass through five of them before pupating.
During the final instar, a caterpillar may increase its body mass by a factor of several thousand compared to its size at hatching. This rapid, continuous consumption stores the vast reserves of energy and nutrients required for the pupal stage. While inside the chrysalis or cocoon, the larval organs break down, and the adult body structures are synthesized from these accumulated resources.
The energy packed into the larval stage must sustain the insect entirely through the non-feeding pupal stage and often provides the bulk of the energy needed by the adult butterfly or moth. This stored energy is used for flight, mating, and egg-laying, especially for species that do not feed heavily, or at all, as adults. A caterpillar’s life is a focused effort to eat enough to fuel a radical biological metamorphosis.
Feeding Safety and What to Avoid
When attempting to provide food for a caterpillar found in the wild, the primary safety consideration is ensuring the plant is the correct, uncontaminated host species. Plant material must be free of pesticides and herbicides, as caterpillars are highly sensitive to these chemicals, which can be lethal even in minute quantities. Many plants purchased from nurseries, even those labeled “pollinator-friendly,” can contain systemic neonicotinoid pesticides that remain toxic to feeding larvae for months.
Avoid offering non-native plants or common grocery store produce, unless the species is confirmed as the exact host plant. A caterpillar will often starve rather than consume a plant it is not adapted to digest. Non-host plants can contain indigestible or toxic compounds that lead to illness or death. If the caterpillar was not found actively feeding on a specific plant, it should not be offered as food.