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BUTTERFLY MORPHOLOGY: Butterflies are insects. And, like most insects, they have (1) a three-parted body (with head, thorax and abomen). They also have two pairs of wings and three pairs of legs on the thorax, and a pair of antennae on the head. In order to describe the anatomy of all life stages of the butterfly, we must look at the varying morphologies of the (1) Caterpillar; (2) Pupa, and (3) Adult.
CATERPILLAR ANATOMY: A caterpillar begins its life as a tiny egg. Many eggs are variously colored and textured with ridges and a variety of patterns characteristic of the species.Normally, within a week, a tiny caterpillars breaks out of the egg covering, eats its nutritious egg shell, and turns into a gluttonous leaf-eating machine. Its elongate body is basically a tube for processing chewed leaves. It has a three-parted body with head, segmented thorax, and segmented abdomen. The head is equipped with a pair or multi-faceted compound eyes for vision. It also has powerful mandibles (jaws) for macerating leaves. The head also bears spinnerets (which may produce silk).The thorax bears three pairs of true legs which allow the caterpillar to crawl, and for holding and manipulating leaf parts which are crushed by the chewing jaws. The legs move by muscles attached to the inside of the exoskeleton. The abdomen has 4 pairs of prolegs (false legs) to support and help move the abdominal segments. Prolegs move by hydraulic pressure. Prolegs have small hook-like suction cups called crochets for holding onto the leaf while eating. Prolegs are not really legs as they have no segments or joints. At the end of the abdomen is a pair of gripping anal claspers. These are used to anchor the caterpillar while the prolegs are doing the walking. The abdomen also has a row of spiracles along each side of the body. These are used for gas exchange (oxygen and carbon dioxide). As the caterpillar continues to eat, it gets larger and larger until its skin splits and is shed. It shakes off the dead skin and reveals beneath it, a new, larger, saggy skin (kind of like a pair of cover-alls that are too large). As it continues to eat and grow, it again grows too large and the skin splits a second time. This skin shedding is repeated about 4 or 5 times in about 2 or 3 weeks. Each stage between shedding, when the caterpillar is active, is called an instar. Often different instar stages of the same species look surprisingly very different. When the final instar stops feeding, it splits down the back and forms a protective covering over itself in which the caterpillar pupates within a hard outer shell. It is now called a chrysalis.
PUPA ANATOMY: The pupal stage is referred to as the chrysalis. The anatomy of the pupae is species-specific. For some species, the pupae may be adorned with spines, knobs, keels, and other bodily extensions. The chrysalis is usually attached to a support (most often a plant). Some chrysalides just drop to the ground among dead leaves. Some butterfly species hibernate in the chrysalis stage during winter and emerge the following spring .The chrysalis may be contorted into odd shapes. Frequently, they resemble twisted, dead leaves, or bits of wood. Others, however, may be smooth and bulbous and quite colorful. They assume a variety of colors, but most tend to blend into the environment to camouflage themselves from predators. Within the pupal chrysalis, a series of tissue destroying enzymes dissolves portions of the caterpillar's body, and re-constructs the body into a butterfly, complete with wings and a nectar sucking proboscis. This dramatic change from a leaf-eating, larval form (caterpillar) to a nectar-sucking, winged adult butterfly is an example of complete metamorphosis. Some people prefer to use the term larva instead of caterpillar. And, many use the terms interchangeably. But, caterpillar is the preferred term to use with butterflies and moths. The term larva (pl. larvae) is best used with insects and other organisms that have a complete metamorphosis.
ADULT BUTTERFLY ANATOMY: The adult butterfly has: (1) a three-parted body (with head, thorax and abdomen). On the head is a pair of antennae, a pair of multi-faceted compound eyes, and a proboscis. The thorax bears three pairs of legs and two pairs of wings (a pair of forewings and a pair of hindwings). While the thorax contains important structures such as the digestive tract, ventral nerve cord, dorsal aorta and tracheae, the majority of the thorax is largely filled with muscles that are used to provide powerful contractions to the legs and wings. The abdomen is usually an elongate cylindrical structure that is composed of eight segments in front of the genital segment (a modification of the original ninth and tenth segments). The progenital segments lack appendages of any kind. These segments enclose and protect the internal organs which include the following: digestive tract, dorsal aorta, ventral nerve cord, the tracheae (breathing tubes), and the reproductive system.