Metamorphosis
Metamorphosis in biology means the process of transformation from an immature form to an adult form in two or more distinct stages. Good examples are insects and amphibians. Life for most insects begins as a larva or nymph then progresses to the pupa stage and ends as an adult.
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[change] Insects
There are two main types of metamorphosis in insects: incomplete metamorphosis or hemimetabolism, and complete metamorphosis or holometabolism.[1]
[change] Incomplete metamorphosis or hemimetabolism
Insects change how they look and what they can do when they grow. Some insects,with incomplete metamorphosis, have three different life stages. These insects start as eggs, which are sometimes so small you cannot see them with the naked eye. When the egg hatches, a larva or nymph comes out. Nymphs are just baby insects. Most of the time, the nymph looks similar to the adult, but it is smaller, may have different coloration, and does not have wings. The nymph grows through stages called instars, shedding its 'skin' (epicuticle) at each stage (ecdysis). Finally, it changes finally into a mature adult with wings.
Some insect nymphs are aquatic, which means they live in water. These nymphs usually have gills and look very different from the adults they will turn into. Nymphs that live in water are called naiads.
Some insects that have a life cycle of egg-nymph-adult are:
[change] Complete metamorphosis or holometabolism
When all insects grow, they change how they look. Insects that have complete metamorphosis have four different life stages. These insects start as eggs, which are very small. The egg hatches and a larva comes out. The larva looks like a worm and eats and eats so that it can grow much bigger. When the larva has grown it changes into a pupa. The pupa usually can not move or eat. The pupa is a special time when the insect is changing into an adult that will look very different from the larva or the pupa. Moth pupae (plural of pupa) are inside cocoons. When the pupa opens, the adult insect comes out.
Many insects have a life cycle of egg-larva-pupa-adult. Some of these insects are:
- Beetles
- Hymenoptera: bees, wasps, ants, sawflies
- Butterflies, moths
- Diptera: the flies
| Species | Egg | Larva/Nymph | Pupa | Adult |
|---|---|---|---|---|
| Housefly | 1 day | 2 weeks | 1 week | 2 weeks |
| Ladybird | 4 days | 2 weeks | 2 weeks | 3-9 months |
| Monarch Butterfly | 4 days | 2 weeks | 10 days | 2-6 weeks |
| Periodical Cicada | 1 month | 13/17 years | no such stage | 2 months |
| Mayfly | 1 month | 3 years | 1 day | |
| Cockroach | 1 month | 3 months | 9 months |
[change] The Monarch butterfly
The Monarch Butterfly goes through four stages of development. Life for a Monarch butterfly begins as an egg hatched from an adult. This egg then develops into a worm-like larva caterpillar. In the pupa or chrysalis stage, the caterpillar spins a silk pad on a twig or leaves and hangs from this pad by its last pair of prolegs. It hangs upside down in the shape of a "J" and then molts leaving it encased in a green exoskeleton. The mature butterfly emerges after about two weeks and feeds on a variety of flowers including milkweed flowers, red clover and goldenrod.
[change] Amphibian metamorphosis
In typical amphibian development, eggs are laid in water and larvae are adapted to an aquatic lifestyle. Frogs, toads, and newts all hatch from the egg as larvae with external gills. Afterwards, newt larvae start a predatory lifestyle, while tadpoles mostly scrape food off surfaces with their horny tooth ridges.
[change] Marine organisms
Marine organisms with a larval stage usually release large numbers of larvae into the water column, where these larvae develop and grow before metamorphosing into adults. Most marine invertebrates and many fish have evolved a life cycle involving a pelagic larval stage or pelagic eggs that have the capacity to be transported long distances.
[change] References
- ↑ Gullan P.J. & Cranston P.S. 2005. Life history patterns and phases in the insects. In An outline of entomology. Blackwell, Oxford. 143-153
- Davies, R.G. Outlines of Entomology. Chapman and Hall: chapter 3
