What makes a butterfly a butterfly? In common with many other insects, adult butterflies have antennae, compound eyes, three pairs of legs, a hard exoskeleton, and a body that is divided into three parts: the head, thorax, and the abdomen. Uniquely, a butterfly's outer body is covered by tiny sensory hairs and the wings are covered by scales.

The head carries many sensory apparati for the butterfly. A butterfly's compound eye enables it to be aware of its immediate surroundings through a large angle. The pair of antennae are clubbed in most butterflies. On the underside of the head is the paired proboscis, which is used to suck nectar from flowers.

The thorax consists of three segments with a pair of legs attached to each segment. The front pair of legs are non-functional and reduced in length in some families of butterflies. The thorax also contains the flight muscles, which are attached to the base of the wings. Internally, the thorax houses the large muscles that control the wings and legs.

The abdomen contains the bulk of the digestive, excretory, and reproductive organs. At the end of the abdomen are the sexual apparati, which contain many characteristics used by taxonomists as an aid in identifying species.

Life Cycle

The life cycle of a butterfly includes four stages: egg, caterpillar or larva, pupa, and adult. The pupa stage is when butterflies undergo a complete metamorphosis. The time needed to complete the metamorphosis varies in each species.

The reproduction process of the butterfly begins with two adults courting and then mating. After mating is complete, the female searches for a location to lay her eggs. It is essential that she finds a place where an appropriate food plant for her larvae is available. Females lay their eggs singly or in groups directly on the underside of the leaf or on the stem of the food plant. Butterfly eggs vary in color, but most tend to be white, green, or yellow, and then change color as the larva develops inside.

When the eggs hatch, the caterpillar enters the first instar (stage of development). Most butterflies experience five instars over a period of three to six weeks. Each time the caterpillar grows bigger, it sheds its skin in a process called molting. After the fifth molting, the caterpillar is usually full grown. It then stops eating and searches for an acceptable place to pupate. It either spins a silken web to fasten the pupa on a firm base or a silken girdle to support the pupa from a stem or a twig. About ten days later, or the next spring for those that hibernate in the winter as pupae, the adult emerges, starting the cycle over.


Migration is found in over 200 butterfly species. Many migrate due to changing seasonal conditions, moving for example to areas that are experiencing a new flush of growth or to areas that are cooler and more moist. Other reasons for migration may include temporary overpopulation and the search for new larval host plants. Two of the most well known migrants are the Monarch (Danaus plexipppus) and the Painted Lady (Vanessa cardui).


Butterflies are recently gaining attention as wildlife worthy of conservation efforts. Attempts to conserve and manage butterfly populations have been initiated by the Federal Endangered Species Act of 1973, as well as many state and provincial acts. Many local jurisdictions and conservation organizations have also taken action to promote the protection of butterflies whose populations are declining. With over 20,000 species of butterflies known, there are only two in the Great Lakes region of the United States that have gained federal protection: the Karner Blue (Lycaeides melissa) and Mitchell's satyr (Neonympha mitchellii).

Butterflies, skippers, and moths

Butterflies, skipper, and moths make up the order Lepidoptera. What distinguishes a true butterfly from a skipper or a moth? In the past, butterflies were distinguished from moths in that they flew during the day, possessed clubbed antennae, were brightly colored, and lacked a frenulum (a wing coupling mechanism found in most moths). There is now a group of tropical American "moths," however, that are thought to be more closely related to butterflies than to moths despite being nocturnal and lacking the clubbed antennae of other butterflies. The classification of skippers has also changed. Traditionally, skippers were considered to be butterflies, but now they are considered to show more similarities to moths due to their small size, thick and hairy body, dull colors, and hooked antennae. These exceptions in the way Lepidoptera are classified suggest that the distinction made between butterflies and moths can be somewhat subjective.


Emmel, Thomas, C.. Butterflies. Alfred A, Knopf, Inc., 1975.

Feltwell, John. The Encyclopedia of Butterflies. Prentice Hall General Reference, 1993.

Grzimek, Bernhard. Grzimek's Animal Life Encyclopedia. Van Nostrand Reinhold Company, 1975.

Opler, Paul, A. A Field Guide to Eastern Butterflies. Houghton Mifflin Company, 1992.


Marie S. Harris (author), University of Michigan-Ann Arbor.


bilateral symmetry

having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.


animals which must use heat acquired from the environment and behavioral adaptations to regulate body temperature