Butterflies And Moths

Type of animal science: Classification

Fields of study: Anatomy, entomology, evolutionary science, invertebrate biology, physiology

Approximately 17,000 species of butterflies and 153,000 species of moths have been classified in the general order Lepidoptera (insects with scaly wings). They exhibit an incredible variety of color, pattern, shape, and size, as well as the ability to adapt to almost every climate.

Principal Terms antennae: a pair of segmented sensory appendages located above the mouth parts Batesian mimicry: an evolutionary trend in which an edible species mimics the form of a distasteful species to avoid predation frenulum: a spinelike device that connects the front and hind wings in moths industrial melanism: the rapid rise in frequency of the melanic form in many moth species downwind of manufacturing sites, associated with the advent of industrial pollution metamorphosis: the process through which a larval form becomes a winged adult form proboscis: a coiled, springlike sucking tube or "tongue" used to drink nectar

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, the Western 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 ex posed 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 lichen-covered 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.

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