Moths eat radically different foods depending on their life stage. As caterpillars, they are eating machines, consuming leaves, wool, beeswax, and even other insects. As adults, most species switch to liquid diets of nectar and other fluids, sipped through a coiled, straw-like proboscis. Some adult moths skip eating entirely, living just long enough to mate on the energy reserves they stored as larvae. The gap between these two life stages is so wide that a single moth species can go from shredding plant tissue with powerful jaws to delicately drinking from a flower, or from nothing at all.
What Most Caterpillars Eat
The overwhelming majority of moth caterpillars are herbivores. Leaves are the staple, and caterpillar species fall along a spectrum from extreme specialists to broad generalists. A specialist caterpillar feeds on just one or a few closely related plant species, while a generalist can thrive on plants from multiple families. Research comparing closely related species has shown that generalists display higher flexibility in their feeding preferences, readily shifting to new host plants when their primary food is unavailable.1Scientific Reports. Higher plasticity in feeding preference of a generalist than a specialist: experiments with two closely related Helicoverpa species Whether specialist or generalist, caterpillars are not mindless eating tubes. They actively regulate the balance of protein and carbohydrates in their diet, adjusting their intake based on what they need for upcoming developmental stages like pupation.2PubMed Central. Fitness of Nutrition Regulation in a Caterpillar Pest Mythimna separata (Walker): Insights from the Geometric Framework
This ability to fine-tune nutrition goes further than just eating more or less. When caterpillars are deprived of protein early in life, they compensate by actively seeking out protein-rich food later. Given a choice between high-protein and high-carbohydrate diets, protein-starved caterpillars select significantly more protein to correct the imbalance.3Animal Behaviour. Caterpillars use developmental plasticity and diet choice to overcome the early life experience of nutritional imbalance They can also adjust their developmental program itself, changing growth trajectories to reduce the damage from an early nutritional deficit. For something with a brain the size of a pinhead, that is a surprisingly sophisticated response to a bad start in life.
How Caterpillars Cope With Toxic Plants
Plants do not sit passively while caterpillars chew through them. Many produce toxic chemicals, including alkaloids, latex, and other defensive compounds. Caterpillars have evolved multiple strategies to deal with these defenses, and some of the tactics are remarkably clever.
On the biochemical side, caterpillars can break down plant toxins using specialized enzymes. The cinnabar moth, for example, feeds on ragwort, a plant loaded with pyrrolizidine alkaloids that are toxic to most animals. The caterpillar produces an enzyme that converts these toxic alkaloids into harmless forms, letting it eat the plant safely.4Journal of Experimental Botany. The bitter truth: how insects cope with toxic plant alkaloids Other caterpillars go a step further: rather than just neutralizing plant toxins, they sequester them, storing the chemicals in their own bodies as a defense against predators. These herbivores use specific transport mechanisms to control where and how the toxins accumulate, and some even boost the toxins’ potency after absorbing them.5PubMed. Sequestration of plant secondary metabolites by insect herbivores: molecular mechanisms and ecological consequences The bright warning colors of many caterpillars are essentially advertisements to birds and other predators: “I taste terrible, and you’ll regret eating me.”
Then there are the behavioral tricks. Many caterpillars that feed on latex-producing plants like milkweeds have learned to cut the leaf veins before feeding. Latex is essentially a sticky, toxic glue that gums up an insect’s mouthparts and poisons it. By severing the veins upstream of where they want to eat, caterpillars block the flow of latex to the feeding site, effectively disarming the plant’s chemical weapon.6PubMed. Vein-cutting behavior: insect counterploy to the latex defense of plants Experiments have confirmed that when researchers surgically cut milkweed veins themselves, even generalist herbivores that normally avoid milkweed can feed on the leaves without trouble. Vein cutting is one entry in a whole catalog of sabotage behaviors that caterpillars use against plants, including trenching (cutting arcs or moats into leaf tissue), girdling stems, and applying fluids from their own glands to neutralize defenses.7PubMed. Behavioral Sabotage of Plant Defenses by Insect Folivores
Caterpillars That Don’t Eat Plants
While herbivory is the norm, some caterpillars have wandered into completely different dietary territory. The clothing moth, whose larvae are the ones responsible for holes in your sweaters, eats keratin, the structural protein found in wool, hair, feathers, and fur. Keratin is one of the toughest natural proteins, and digesting it is something almost no animal can do on its own. Clothing moth caterpillars manage it partly through gut chemistry: their midgut maintains an oxygen-free, highly reducing environment that helps break apart keratin’s tough molecular bonds. They also harbor gut bacteria that secrete cocktails of enzymes specifically adapted to keratin digestion.8PubMed Central. Larvae of the Clothing Moth Tineola bisselliella Maintain Gut Bacteria that Secrete Enzyme Cocktails to Facilitate the Digestion of Keratin This partnership between the caterpillar’s unusual gut conditions and its microbial residents is what makes wool-eating possible.
Another oddity is the greater wax moth, whose caterpillars feed on beeswax inside honeybee hives. Beeswax is a complex polymer of esters and hydrocarbons, and breaking it down requires an unusual digestive toolkit. The caterpillars rely on gut microbes that can degrade these waxy compounds.9Folia Microbiologica. Characterization of the gut microbes of greater wax moth (Galleria mellonella Linnaeus) shows presence of potential polymer degraders The chemical bonds in beeswax are similar to those in common plastics like polyethylene, a fact that has attracted intense scientific interest for biotechnology applications (more on that later).
Then there are the genuinely predatory caterpillars, which are strikingly rare. Across all roughly 200,000 known moth and butterfly species, predatory caterpillars make up less than about a tenth of one percent. Hawaii, an evolutionary hotspot for unusual insects, is home to some of the most dramatic examples. One recently described Hawaiian species lives inside spider webs, feeding on the arthropod prey trapped there, and decorates its portable larval case with the body parts of the spiders it kills.10Science. Hawaiian caterpillar patrols spiderwebs camouflaged in insect prey’s body parts Other Hawaiian caterpillars are ambush predators that snatch flies with modified front legs. These species evolved on islands with few competing predators, which likely opened the door for caterpillars to fill ecological roles normally occupied by spiders and other hunters.
How Adult Moths Feed
When a caterpillar pupates and emerges as an adult moth, its entire feeding apparatus has been rebuilt. The chewing mandibles are gone, replaced in most species by a proboscis: a long, coiled tube formed from two interlocking halves that together create a sealed food canal. This structure functions as a drinking straw, with fluid uptake powered by a muscular sucking pump inside the moth’s head.11PubMed Central. Feeding mechanisms of adult Lepidoptera: structure, function, and evolution of the mouthparts For most moths, the primary food source is flower nectar, a sugar-rich liquid that provides the energy needed for flight, mating, and egg production.
The proboscis is more than just a straw, though. Research on its microstructure has revealed a hierarchical system of pores spanning from nanoscale to microscale, which promotes capillary action and lets the proboscis pull liquids from a wide range of surfaces, not just the deep wells of flowers.12PubMed Central. Butterfly proboscis: combining a drinking straw with a nanosponge facilitated diversification of feeding habits This sponge-like capability is thought to have been a key factor in the diversification of feeding habits across moths and butterflies, allowing different lineages to exploit rotting fruit, tree sap, dung, and other liquid or semi-liquid food sources beyond nectar.
Mud-Puddling and the Quest for Minerals
If you have ever seen a cluster of moths or butterflies gathered on a muddy riverbank, a puddle, or even a sweaty backpack, you have witnessed puddling behavior. These insects are not drinking for water; they are mining for minerals, especially sodium. Nectar and plant tissues are generally low in sodium, and adult moths that rely heavily on nectar can find themselves deficient in this essential mineral.
The behavior has been studied in detail in the moth Gluphisia septentrionis, where males drink from mud puddles to accumulate sodium. Chemical analyses of the moths’ bodies confirmed that puddling leads to real systemic sodium gains. The acquired sodium is then transferred to the female during mating, packaged as a nuptial gift for eventual incorporation into the eggs.13PubMed Central. Sodium: a male moth’s gift to its offspring This makes biological sense: the moths’ larval food plant is low in sodium, so providing a sodium boost to the next generation gives offspring a head start.14PubMed. Sodium uptake by puddling in a moth Puddling is predominantly a male behavior across many moth and butterfly species, and the sodium-gift hypothesis helps explain why males are so much more commonly seen doing it.
Tear-Drinking and Other Surprising Liquid Diets
Some adult moths have taken mineral-hunting to an extreme by drinking the tears of large animals. This behavior, known as lachryphagy, has been documented across multiple moth species feeding on the tears of cattle, deer, and other mammals. The tears provide sodium and proteins that the moths cannot get from nectar alone.15Ecosphere. Observations of tear‐drinking by lepidopterans on moose (Alces americanus americanus) in northeastern North America Observers have reported moths landing near the eyes of sleeping or resting animals and feeding on lachrymal secretions, sometimes causing irritation to the animal’s eye tissues.16Medical and Veterinary Entomology. Moths and Butterflies (Lepidoptera)
A handful of moth species in the subfamily Calpinae have gone even further, using a stiffened, barbed proboscis to pierce fruit skin and drink the juice. At least one species in this group, Calyptra thalictri, has been documented piercing mammalian skin and drinking blood under experimental conditions. These so-called “vampire moths” are a curiosity rather than a public health concern, as blood-feeding appears rare and opportunistic in the wild. But the progression from fruit-piercing to skin-piercing is a fascinating example of how a feeding structure adapted for one purpose can be co-opted for another.
Adults That Never Eat
Not all adult moths bother with feeding at all. The luna moth, one of the most recognizable moths in North America, emerges from its cocoon without functional mouthparts. It has no proboscis, no way to eat or drink, and lives for roughly a week on the fat reserves it accumulated as a caterpillar. Its only goal as an adult is reproduction. The same is true of many silk moths in the family Saturniidae, as well as certain other groups. These species have essentially front-loaded their entire lifetime’s energy intake into the caterpillar stage, treating adulthood as a brief, focused reproductive sprint.
This strategy makes more evolutionary sense than it might seem. Building and maintaining complex feeding structures has costs, and for a large-bodied moth with substantial fat reserves, the energy savings from not feeding may outweigh the potential gains from a few days of sipping nectar. The trade-off works especially well for species that emerge as adults synchronously in large numbers, because finding a mate quickly is more important than fueling a long life.
When Caterpillar Feeding Reshapes Ecosystems
Because caterpillars are such prolific eaters, outbreaks can reshape entire landscapes. In sub-arctic Scandinavia, periodic population explosions of geometrid moth caterpillars strip birch forests of their leaves. Research following defoliation events has shown that the effects ripple far beyond the trees themselves. Soil respiration drops, inorganic nitrogen accumulates in the soil, and the community of fungi that partners with tree roots shifts toward less energy-demanding species.17Ecosystems. Slowed Biogeochemical Cycling in Sub-arctic Birch Forest Linked to Reduced Mycorrhizal Growth and Community Change after a Defoliation Event In other words, when caterpillars strip a forest canopy, the below-ground nutrient cycling slows to a crawl. The whole system shifts into a lower gear, and recovery can take years.
On a smaller scale, caterpillar feeding is a fundamental link in food webs everywhere. Caterpillars are among the most important food sources for nesting birds, and the timing of caterpillar availability in spring can determine whether bird chicks get enough protein to survive. Gardeners and farmers, of course, experience caterpillar feeding as pest damage, and moth caterpillars are responsible for enormous crop losses worldwide. The same voracious appetite that makes caterpillars ecologically important makes them economically devastating when the species in question feeds on cotton, corn, or stored grain.
Wax Moths and Plastic-Eating Potential
The greater wax moth’s ability to digest beeswax has led to one of the more unexpected research stories in recent years. Because the chemical bonds in beeswax resemble those in polyethylene, researchers tested whether wax moth caterpillars could break down plastic. Early experiments confirmed that the caterpillars could degrade polyethylene at a remarkably fast rate, generating excitement about potential biotechnological applications for plastic waste management.18Current Biology. Polyethylene bio-degradation by caterpillars of the wax moth Galleria mellonella
Follow-up research pinpointed the mechanism more precisely. Two enzymes in the wax moth caterpillar’s saliva, belonging to the phenol oxidase family, can oxidize polyethylene on their own, without needing the caterpillar’s gut or its microbes. These are the first animal enzymes ever identified with this capability.19Nature Communications. Wax worm saliva and the enzymes therein are the key to polyethylene degradation by Galleria mellonella The practical path from lab demonstration to industrial-scale plastic recycling remains long and uncertain, but the work illustrates how studying an obscure moth’s diet can produce discoveries with implications well beyond entomology. A pest that beekeepers have cursed for centuries may end up contributing to one of the most pressing environmental problems of our time.
What Household Moths Are Actually After
For most people, the practical question about moth diets comes down to household damage. Two groups of moths cause the bulk of domestic trouble, and they eat very different things.
Clothes moths, primarily the webbing clothes moth and the casemaking clothes moth, are after keratin. Their caterpillars feed on wool, silk, cashmere, fur, feathers, and similar animal-based fibers. They can also damage blends that contain a percentage of animal fiber. Cotton, polyester, and other purely plant-based or synthetic fabrics are not at risk unless they are soiled with food stains or body oils, which the larvae may consume along with the fabric. The adult clothes moth does not eat anything; it has reduced mouthparts and lives solely to reproduce. The damage is entirely done by the larval stage, often hidden in dark, undisturbed areas of closets or drawers.
Pantry moths, including the Indian meal moth, are a separate problem. Their caterpillars eat stored dry goods: flour, rice, cereal, dried fruit, nuts, pet food, and birdseed. They contaminate food with silk webbing and frass. The adults, again, are not the ones eating your groceries. Seeing a small moth fluttering near your kitchen ceiling usually means caterpillars are already at work somewhere in your pantry. Controlling either type requires targeting the larvae, since the flying adults you notice are just the visible tip of the problem.