Like butterflies, moths change in form as they develop into adults. Only the adult form of a moth has wings. Female adult moths lay many tiny eggs that hatch into wormlike caterpillars. A caterpillar eats almost constantly, and it grows rapidly. After it is fully grown, the caterpillar forms a shell-like covering around itself. Within this shell, the insect goes through its final changes. Eventually, the insect breaks out of the shell as a fully developed adult moth.

Moths differ from butterflies in a number of important ways. For example, most moths fly at dusk or at night. The majority of butterflies fly during the day. Among most moths, the hind wing is attached to the front wing by a hook or set of hooks, called a frenulum. Butterflies lack a frenulum. In addition, most butterflies have antennae that widen at the ends and resemble clubs. The antennae of most moths are not club-shaped.

Some moths are regarded as pests because their caterpillars feed on and damage trees, food plants, or clothing. However, many others are valuable to people and nature. People use caterpillars of certain moths to produce silk. Many adult moths help pollinate flowers.

The Bodies of Moths

A moth's body, like that of any insect, has three main parts. They are: (1) the head, (2) the thorax, and (3) the abdomen.

The head bears the moth's eyes, antennae, and mouthparts. These structures are the insect's most important sense organs.

Eyes. Moths have two large compound eyes on each side of the head. These eyes consist of many separate lenses, each of which supplies a complete image of part of the moth's surroundings. Compound eyes are specially designed to help an insect spot movements, such as the approach of an enemy.

Antennae. Two antennae stick out from between a moth's eyes. Moths use their antennae chiefly to smell. The antennae are extremely sensitive to chemicals in the air. Female moths release chemicals called pheromones into the air to attract males for mating. The antennae of a male moth can "smell" a female as far as 5 miles (8 kilometers) away.

Mouthparts. Adult moths feed mostly on liquids, such as flower nectar and the juice of fruits. They suck up their food through a long, hollow tongue called a proboscis. The proboscis coils under the head when not in use.

The Thorax forms the middle section of a moth's body. Attached to the thorax are the legs and wings of the insect.

Legs. Adult moths have three pairs of legs. Each leg consists of five segments. Joints connect the segments. Taste organs grow at the tips of the legs.

Wings. Two membranes form each of a moth's wings. A network of hollow tubes called veins supports the wings. Tiny scales cover the membranes and give the wings their colors and patterns. The females of some species lack wings and cannot fly.

The Abdomen contains the organs of reproduction and the major organs of digestion. Tiny holes called spiracles on the sides of the abdomen lead into the insect's respiratory system. Oxygen enters the moth's body through the spiracles.

The life cycle of moths

Every moth goes through four stages of development: (1) egg, (2) larva, (3) pupa, and (4) adult. The process of development through several different stages is called metamorphosis.

The egg. Female moths lay their eggs one at a time or in masses, usually in summer or fall. A female moth may lay from a few to more than 18,000 eggs. Most moth eggs measure less than 1/25 inch (1 millimeter) across and are round or oval. Often, the female deposits the eggs on the kinds of plants that her offspring like to eat. The eggs of most species hatch within a week. The eggs of some species do not hatch until spring.

The larva, or caterpillar, that crawls out of the egg is made up of 14 segments, including a head. Caterpillars have three pairs of legs near the front of the body. Most caterpillars also have five pairs of leglike prolegs, farther back on the body. Many moth caterpillars are extremely colorful, and some have fierce-looking spines or bristles.

Caterpillars have chewing mouth parts. Moth caterpillars chiefly eat leaves and other plant parts. They may also feed on wood, the larvae of other insects, and hair. Many moth caterpillars feed on clothing and other materials made of wool, which is sheep's hair.

A short structure called the spinneret sticks out below the mouth. The caterpillar sends out an almost continuous stream of liquid silk through the spinneret. The silk quickly hardens to a slender thread that gives the caterpillar a foothold as it crawls about.

Caterpillars grow to their full size within a month or several months, depending on the species and other factors. Like other insects, they shed their skin several times as they grow. This process is called molting.

The pupa. The final molt transforms the caterpillar into a pupa, an inactive stage during which dramatic physical changes occur. The caterpillar may spin a protective, silken cocoon around itself for the pupal stage. The insect fastens the cocoon to a tree limb or some other solid object. Inside the cocoon, the insect forms a protective shell of a substance called chitin. Some moth caterpillars do not spin cocoons. Instead, they burrow into the ground or hide under loose bark before forming a chitin shell.

During the pupal stage, the insect does not move about. But within the chitin shell, the wormlike caterpillar changes into an adult moth. This change, called pupation, takes a few days or several months, depending on the species.

The adult. At the end of pupation, the adult moth breaks out of its chitin covering. If the moth has wings, it pumps blood into the wings to expand them and soon flutters off in search of food or a mate. Most adult moths live only a few days to a few weeks, but some may survive six months or more. A few adult moths do not feed and live only a few days.

The importance of moths

The best-known benefit of moths to human beings is probably the production of silk. In China, people have used a species of moths called Bombyx mori to produce silk for more than 4,000 years. To obtain the silk, workers unravel the moth's cocoon into a single, long thread. The thread is then combined with thread from other cocoons and woven into silk fabrics.

Moths are important in the pollination of certain flowers. Pollination occurs when a moth visits flowers to feed on nectar. Grains of pollen stick to the moth's body as it feeds and then rub off on other flowers the insect visits. Some flowers that bloom only at night depend on night-flying moths for pollination.

Moth caterpillars eat leaves and other plant parts. They cause extensive damage to crops and forests each year. Some species feed on woolen fabrics and other animal products. The caterpillars of a group of moths known as clothes moths may damage woolen garments.

return to top