What Is a Butterfly?

Butterflies, like all plants and animals, are placed in a hierarchical classification that expresses their relationships in increasing levels of resolution. They belong to a group of animals called arthropods (Phylum Arthropoda), which have segmented bodies, jointed legs, and a supporting skeleton derived from the hardened, chitinous skin, termed an exoskeleton. The most common groups of arthropods are insects, spiders, and crabs. Within the arthropods, butterflies belong to a subgroup, the insects (Class Insecta), characterized by a three-part body (head, thorax, and abdomen) and three pairs of jointed legs on the thorax. Within the insects, butterflies, together with the moths, combine to form a group called the Order Lepidoptera. The closest relatives of the Lepidoptera are the caddis flies (Order Trichoptera).

The Lepidoptera, along with other orders of 'higher' insects, such as the beetles (Coleoptera), flies (Diptera), and wasps (Hymenoptera), have four stages to the life cycle - egg, larva, pupa, and adult - usually referred to as complete metamorphosis. Lepidoptera larvae have a characteristic shape and structure and are commonly called 'caterpillars'. Similarly, the pupae of butterflies are often ornamented with spines and bumps and are commonly called chrysalises (singular chrysalis).

The Lepidoptera are best characterized by having four wings that are covered with flat, shingle-like scales that give the wings their colour and pattern, but they are also characterized by a large number of less obvious structural characters including the presence of a comb-like structure on each front leg, called an epiphysis, that is used for cleaning the antennae. The epiphysis is present in most moths but is retained only in the more primitive families of butterflies (i.e., Papilionidae and Hesperiidae).

Most people, and the historical classification of the Lepidoptera, arrange the Lepidoptera into two groups: butterflies and moths. Although this division is useful and popular, we now know that it does not accurately reflect the relationships of the groups within the Order Lepidoptera, since butterflies are most closely related to a small number of families of moths that make up part of a group of families commonly called the "Macrolepidoptera". For a more detailed and technical review, see Lepidoptera classification.

© 2003. Reproduced with permission from The Butterflies of Canada by Ross A. Layberry, Peter W. Hall, and J. Donald Lafontaine. University of Toronto Press; 1998. Specimen photos courtesy of John T. Fowler.