Metamorphosis in animals

   Metamorphosis is the change in body form and structure which takes place in some animals as they develop from young (larvae) to adult. The word "metamorphosis" comes from a Greek word which means "to transform." Grasshoppers, termites, dragonflies, damselflies, and frogs go through an incomplete meta­morphosis in which there is a partial change of body form. Bees, beetles, flies, fleas, moths, butterflies, and doodlebugs go through a complete metamorphosis in which there are three stages of change m body form and structure. These three stages are: larva, pupa, and adult.

   Baby grasshoppers are called nymphs, and undergo incomplete metamorphosis. With their six legs and compound eyes, they look somewhat like adult grasshoppers, except for their wings. The nymph's wings grow very slowly, getting a little bigger each time the nymph molts (sheds its outer covering). The wings are not fully developed until the grasshopper has reached the adult stage.

   The life cycle of the frog is generally used as an example of incomplete metamor­phosis among animals. In the spring the female frog lays eggs in a pond or stream. Frogs in the form of tadpoles hatch from these eggs. Tadpoles have long tails and no legs. They breathe by means of gills and must live in water. After a period of time, the tadpoles gradually begin to lose their gills and tails, to develop legs and lungs, and to take on the form of adult frogs. Changes also take place inside the bodies of the tadpoles. They do not eat during this period of change.

   The life cycle of a butterfly is an example of complete metamorphosis. The adult female butterfly lays eggs on the leaf of a plant. From these eggs emerge butterflies in the form of crawling larvae called caterpillars. The caterpillars have many legs, biting jaws, and no wings. They may be brown, yellow, white, or green with black rings.

   They eat and grow for about two months, shedding their skin (molting) many times as their body increases in size. The butterflies, still in the form of caterpillars, then form a smooth hard case (chrysalis) about themselves and hang from a twig or leaf. The larvae of some insects, such as the moth, spin a thick web called a cocoon about their bodies, fastening themselves to a twig or rough spot. This is the pupa stage. They emerge as adults.