Lepidoptera

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

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).

Con­ser­va­tion

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.

Ref­er­ences

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.

Con­trib­u­tors

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

Glossary

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.

ectothermic

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