A metamorphosis is a great change in form during the life cycle of an animal or insect. A wonderful example of metamorphosis is a caterpillar turning into a butterfly. The two even exist in different habitats after the change. The two forms look totally different.
Like many other insects, butterflies have four stages in their life cycle. The mother butterfly lays tiny eggs somewhere on a plant. The plant must be just the right type because once the caterpillars hatch, they must have the right food to eat. A larva comes out of the egg. In the case of a butterfly, the larva is called a caterpillar. The caterpillar starts eating right away and gets very big. It must shed its skin five or six times. This process is molting. Between the molting times are periods called instars.
The caterpillar gets ready for a transformation or metamorphosis (a change) within a few weeks. It spins a little pad of silk and attaches himself to it upside down. When it sheds its skin again, a pupa is revealed. The pupa of a butterfly is a chrysalis. The outside of the chrysalis hardens to protect the pupa. Inside the pupa, the caterpillar is eating some of its own body. Little parts of the future butterfly have been inside the caterpillar's body. A hormone gives the signal, and they grow into wings, legs, antennae, and proboscis. When the adult butterfly comes out, it weighs about one-half of the weight of the original caterpillar.
Other insects go through the four-stage life cycle also: the egg, larva, pupa, and adult. Each one has different ways of doing this. After a queen bee lays an egg in each cell, adult honeybees feed the larvae inside the hive. Five days after the egg hatches, the larvae are ready to experience a metamorphosis or be changed. The adults seal the larvae into cells. The larvae spin cocoons by turning somersaults inside the cell. After thirteen days, the adult honeybees chew their way out of the cells.
Twelve percent of all insects have a three-stage life cycle: egg, nymph, and adult. They go through simple metamorphosis. They have no resting stage. The nymph hatches out of the egg looking something like the adult. As it molts, it looks more and more like the adult.
Dragonflies go through a three-stage metamorphosis of egg, nymph, and adult. This metamorphosis is very dramatic. When the eggs hatch, they look like tiny beetles. However, they can breathe underwater because they have gills. The nymph may molt eight-fifteen times in the water. For its last molt, the nymph drags itself out of the water onto a plant. It starts pumping a liquid substance into its little wing buds and soon the wings emerge and allow the insect to fly away. Sometimes the molting stage of an insect may be triggered by temperature or a change in season. All the nymphs of one type of insect may be transformed on the same day in the same pond.
Frogs have a three-stage life cycle which is a little different. It is egg, larva, and adult. The mother frog lays the eggs in a pond or body of water. When they hatch, little tadpoles appear which can swim. Soon, legs and lungs form, and the tail shrinks. Its mouth gets wider. The adult frog jumps out of the water and can live on land. Its new legs can leap great distances.
Jellyfish are just little planulae (free-swimming larvae with flattened bodies) swimming around in the water. They change into a cup-shaped polyp which has a mouth and tentacles. The polyp sits around trapping food until a change in the temperature of the water causes it to start shooting off little discs of new jellyfish. This is called 'budding off.' The discs grow into adults. The adult form is called a Medusa because it looks like the head of the Gorgon Medusa in Greek mythology who had snakes for hair.
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