Moths belong to the insect order Lepidoptera, which includes over 160,000 described species worldwide. Understanding their diet is complicated by their life cycle, which involves complete metamorphosis with four distinct stages. A fundamental difference in feeding behavior exists between the immature larval form and the adult form. The larval stage is dedicated almost entirely to mass consumption and growth, while the adult stage is primarily focused on reproduction, resulting in vastly different diets and feeding mechanisms.
How Adult Moths Obtain Energy
The primary purpose of an adult moth is to reproduce, meaning their energy requirements are minimal compared to the larval stage. Most adult species feed exclusively on high-energy liquids, which they draw up using a specialized mouthpart called a proboscis. This long, tubular structure remains coiled like a watch spring beneath the head when the moth is not actively feeding.
To consume liquids, the moth unfurls the proboscis using fluid pressure, extending it into a source like floral nectar. This positions many moths as important nighttime pollinators. They also seek out tree sap, the juices of fermenting or rotting fruit, and water droplets for hydration. A few basal moth families, such as the Micropterigidae, are exceptions, possessing functional mandibles that allow them to chew and consume pollen.
Many prominent moth species do not feed at all during their adult stage, relying entirely on fat reserves accumulated as larvae. Species like the Luna moth and Polyphemus moth have vestigial, or non-functional, mouthparts. Because they cannot replenish energy stores, these adults live for only a few days or weeks, sustaining themselves just long enough to locate a mate and lay eggs.
The Diverse Diets of Caterpillars
The larval stage, or caterpillar, is the main feeding stage in the moth’s life cycle, driven by the need for explosive growth before metamorphosis. Caterpillars are equipped with strong mandibles for chewing and can increase their body mass thousands of times before pupating. The vast majority of moth larvae are herbivores, primarily consuming the leaves of vascular plants.
Moth caterpillars exhibit a wide spectrum of dietary habits, ranging from highly specialized feeders to generalists. Specialists are restricted to feeding on only one or a small group of related host plants, requiring the female moth to lay eggs only on those specific plants. Generalists are capable of consuming foliage from dozens of different plant families, allowing them to thrive in diverse ecological settings.
Beyond leaves, the natural diets of caterpillars include a variety of materials. Wood-boring larvae tunnel through and consume the xylem and phloem of trees, while others feed on stems, roots, seeds, and flowers. Some caterpillars are detritivores, consuming decaying plant matter, fungi, or animal detritus. A few rare species are predators, actively hunting and consuming other small insects.
Identifying Moths That Consume Household Goods
A very small fraction of moth species have adapted to consume materials found in human-built environments, leading to their classification as common household pests. These species are divided into two main groups based on their specific food source, which is always consumed by the larval stage.
Pantry moths, such as the Indian meal moth (Plodia interpunctella), target dried, starchy, and grain-based products. Their larvae infest and feed on cereals, flour, rice, pet food, nuts, dried fruits, and spices, often leaving behind fine, silken webbing. The larvae seek out these substances for their high concentration of carbohydrates and starches, which fuel their rapid development.
Clothes moths, including the webbing clothes moth (Tineola bisselliella), are chemically attracted to animal fibers because they possess the digestive enzymes needed to break down keratin. Keratin is a tough protein found in hair, feathers, and skin, making natural materials like wool, silk, fur, felt, and leather the primary targets of the larvae. They will also chew through synthetic fabrics if they are soiled with perspiration, urine, or food stains, as these deposits provide moisture and additional nutrients.