Butterflies and moths

Butterflies and moths are collectively the second largest order of the insect class and are found on nearly every continent. Over 170,000 species have been classified and new species continue to be identified each year. While some are known throughout the world, most lepidopteran species have more limited distributions that reflect the presence of geographic barriers (such as mountains or deserts), food plant distribution, strength of flight, and degree of tolerance to environmental factors (such as temperature). Like other animal species, butterflies and moths exhibit their greatest diversity in the tropics.

Physical Characteristics of Butterflies and Moths
Butterflies and moths exhibit an enormous diversity of physical attributes. The smallest, theWestern pygmy blue, is a butterfly with a wingspan of just 1.5 centimeters; the largest, the Atlas moth, has a wingspan that can reach 30 centimeters. Like all insects, the bodies of butterflies and moths are divided into three regions: head, thorax, and abdomen. In most species, the head has prominent, large, compound eyes and a long pair of antennae used as "feelers" mounted above. Lepidopterans also have well-developed olfactory organs, and some moths are capable of hearing. Below the eyes is a coiled proboscis used to suck nectar. The thorax of the insect has three segments, each of which bears a pair of legs, the last two of which support pairs of wings, referred to as the fore and hind wings, respectively. The wings of butterflies and moths are supported by a series of tubular struts, called veins, that form complex patterns, which are often of great taxonomic significance in distinguishing species. The abdomen is a roughly tubular structure composed of ten segments ending with external genitalia which, because they vary greatly from species to species, are also of great taxonomic significance. The entire body, with the exception of the eyes, is covered with fine hairs, some of which are flattened to form scales. On the wings these scales are arranged like the shingles on a roof, with the exposed surface having minute longitudinal ridges visible under a microscope. Lepidopterans vary greatly with respect to wing color and pattern.Wing coloration is usually caused by pigments deposited in the scales of the wings, but in some butterflies, such as the purple emperor, the iridescent and metallic colors are due to the construction of the scales themselves. Many butterflies are highly prized for their beautiful and brilliantly colored wings, including the blue morpho, whose brightly colored blue wings are thought to play an important role in mate attraction. In other species a conspicuous pattern may serve as warning coloration. One well-known example is the monarch butterfly, which has a bold pattern of black and orange that warns potential predators that it is distasteful. In this case, the warning is accurate because monarchs feed on milkweed plants that secrete a distasteful substance. It is interesting to note that the viceroy butterfly has evolved a nearly identical wing pattern, apparently to fool potential predators into thinking it is a monarch. The latter is an example of Batesian mimicry, or the evolution of form similar to a distasteful model by an edible species. Coloration, pattern, wing size, and shape in other species may, conversely, aid the lepidopteran by rendering it inconspicuous. For example, the pale form of the peppered moth is actually a complex pattern that effectively camouflages it against lichencovered tree trunks. While butterflies and moths are physically quite similar to one another, there are several distinct structural features used by taxonomists to distinguish them. Butterflies have antennae that are clubbed or at least swollen at one end, whereas the antennae of most moth species are featherlike. Butterflies all lack a true frenulum, which is a device that connects and coordinates the movement of the fore and hind wings of moths during flight. In general, butterflies have slender bodies, are brightly colored, and fly during the day, whereas moths are stouter, exhibit more drab colors, and fly at night. There are, however, some brightly colored, slender moth species, such as the coppery dysphania, and some representatives of one of the butterfly families known as "skippers" have stouter bodies, are dull-colored, and may be active at night.

The Life Cycle of Butterflies and Moths
Butterflies and moths share a complex life cycle consisting of four distinct phases: egg, caterpillar (larvae), pupa, and adult. After mating, the female lepidopteran lays eggs, sometimes singly and sometimes in clusters, on the food plant of the caterpillar or larvae. After hatching, the larvae usually feed on the plant's leaves, although in some species, such as the skippers, the larvae feed on the stems and roots of the plant. During this time the larvae grow rapidly and shed their old skin or exoskeleton four or five times before they are fully grown. Upon reaching full size, the caterpillar undergoes a dramatic transformation, called metamorphosis, into a quiescent pupa or chrysalis stage, during which the larval organ systems are dissolved and rebuilt into the structures of the adult moth or butterfly. The caterpillar begins this process by spinning a small button of silk from which it hangs head downward. While grasping the shed larval skin between the edges of its abdominal segments, the pupa fastens itself to the button of silk. In some species, such as the swallowtails, the pupa is held upright by means of a silk girdle around its middle; in other species, such as the skippers, the larvae pupate in cocoons. After a period ranging from a few weeks to years, the lepidopteran emerges from the chrysalis and expands its wings by pumping blood into them from the body cavity. When the wings have dried, the lepidopteran is ready for flight. Several lepidopteran species undergo migration. In some species, such as the monarch butterfly, the adult migrates on a seasonal basis. Experimental releases of monarchs suggest it is unlikely that any of the adult butterflies who start the journey complete the round trip-it is thought that the journey back is completed by their offspring.

Beneficial and Destructive Butterflies and Moths
Butterflies and moths play essential roles in the pollination of many plant species, are important sources of food for other animals, and are highly valued for their aesthetic qualities by collectors. Larvae of the silkworm moth have been used to produce silk in China since 2640 b.c.e. Several lepidoptera, however, are pests of important agricultural crops. The larvae of the cabbage butterfly do millions of dollars of damage to the cabbage crop each year; gypsy moth larvae are notorious for defoliating trees in North America and Eurasia.