Moths, like all insects in the order Lepidoptera, undergo a complete transformation process known as holometabolism. This life cycle features four distinct stages: egg, an immature stage focused on feeding, an inactive stage of reorganization, and finally, the winged adult. The second stage is a highly recognizable form that bears little resemblance to the flying insect. This period of rapid growth and consumption is the stage most people encounter.
The Universal Terminology
The most general and scientifically accurate term for the immature stage of a moth is the larva. This designation applies across the entire insect world to the young of any species that undergoes complete metamorphosis. The common name universally used for the larvae of both moths and butterflies is caterpillar. This term is specific to the order Lepidoptera and is widely recognized. The caterpillar is the only stage in the moth’s life cycle capable of causing structural damage to plants or household goods.
Distinguishing Features of Moth Larvae
Moth larvae possess a characteristic body structure that separates them from the young of other insect types. Their body is divided into three sections, utilizing two different types of legs for movement. The three segments directly behind the head (the thorax) each bear a pair of short, jointed appendages called true legs. The remaining abdominal segments feature fleshy, unjointed appendages known as prolegs. Most moth caterpillars have a maximum of five pairs of prolegs, typically located on the third through sixth abdominal segments and a final pair at the rear. This specific arrangement (three pairs of true legs and five or fewer pairs of prolegs) distinguishes moth larvae from sawfly larvae, which have prolegs on six or more abdominal segments.
Life Stage and Development
The primary function of the larval stage is to feed and accumulate energy stores for the subsequent stages of the moth’s life. The caterpillar is often described as a dedicated eating machine, consuming large quantities of food to rapidly increase its size and mass. This intense feeding is necessary because the adult moth form often has a mouth structure designed only for sipping liquids, or in some species, no functional mouthparts at all. As the larva feeds, its rigid outer skeleton, called an exoskeleton, restricts its growth, requiring the caterpillar to shed its entire skin in a process called molting. The period between each molt is referred to as an instar, and most species pass through four to five instars before reaching full size.
Common Moth Larvae of Concern
Many people encounter moth larvae inside their homes, where two specific types cause common problems. The larvae of the Webbing Clothes Moth digest keratin, a protein found in animal fibers, feeding exclusively on materials like wool, silk, fur, and cashmere. They cause damage to stored clothing and natural fiber rugs, often creating silken tubes or patches of webbing as they consume the material. The other common household pest is the Indian Meal Moth larva, often called a pantry moth. These larvae feed on dried plant products such as grains, cereals, flour, dried fruit, and pet food, with infestations identified by fine, silken webbing that binds food particles together.