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LIFE CYCLES - DIFFERENCE AS USED FOR INSECT IDENTIFICATION

Life cycle refers to the process insect generations go through from adult stage to adult stage and the various changes they go through. These changes, called metamorphosis, are different for various insects. However, we can group them into similar types of metamorphosis. They are no metamorphosis, gradual metamorphosis, incomplete metamorphosis, and complete metamorphosis.

NO METAMORPHOSIS

In this life cycle, there are virtually no changes in the insect appearance from young to adult except for size and sexual maturity. The stages of this life cycle include:
  • Egg
  • Young
  • Adult
The insect grows through a series of molts where it sheds its outer skin in order to grow larger. The feeding habits are the same for the young and the adult.

Silverfish are an example of an insect that has this type of life cycle.

GRADUAL METAMORPHOSIS

In this life cycle, there is a metamorphosis in the insect as it develops. The stages in this life cycle include:
  • Egg
  • Nympth (with several Instars)
  • Adult
These insects mature through molts, very similar to that of the no metamorphosis group, with the food preferences and appearance being very similar between the young nymphs and the adults. However, as the insect matures into an adult, they do develop wings or wing pads.

Examples of insects with this type of life cycle includes cockroaches, termites, bedbugs, and earwigs.

INCOMPLETE METAMORPHOSIS

With this type of life cycle, the insect's metamorphosis is greater than that of gradual metamorphosis. The stages in this life cycle include:
  • Egg
  • Naiad
  • Adult
These insects have different body structures as naiads than as adults. Naiads are adapted for living in water, while the adults live on dry land and can fly. Their wings are only developed in the last stage of growth; the adult.

Examples of insects with this type of life cycle include dragonflies, damselflies, and mayflies.

COMPLETE METAMORPHOSIS

With this type of life cycle, the young and the adult forms have vastly different body structures and habits. The stages for this life cycle include:
  • Egg
  • Larva
  • Pupa
  • Adult
The larvae, which emerge from the egg, are vastly different from the adult in structure, feeding habits, and movement. Some, such as maggots (larvae of flies), are worm-like creatures. Some, like the carpet beetle larvae, have legs on the thorax but no abdomen. Some larvae have gills that enable them to live under water. Wings are not present and they usually have very simple eyes. In insects where they cause damage, it is usually the larvae that cause the damage.

As the larvae grow, they move into the pupal stage. Sometimes, this involves the creation of a cocoon while other will just stop movement. It is during this stage that dramatic changes occur to the insect. The legs, wings, and the antennae become fully developed.

Out of the pupal stage comes the adult. There is no growth of the insect after it emerges from the pupal case. These insects now differ from the larvae by size and form, by being sexually mature, and by usually having two pairs of wings. They, in fact, usually look completely different from the larvae.

Examples of insects with this type of metamorphosis are beetles, moths, butterflies, fleas, flies, ants, bees, and wasps.

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