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Holometabolism, also called complete metamorphism, is a term applied to insect groups to describe the specific kind of insect development which includes four life stages - as an embryo or egg, a larva, a pupa and an imago or adult. Holometabolism is a monophyletic trait that all insects in the Endopterygota superorder have. This type of development gives the offspring the unique advantage of not competing with adults because they inhabit different ecological niches due to the morphological differences in the different stages of their life cycle.
There are four developmental stages, each having different morphology.
The first stage is from the fertilization of the egg inside the mother until the embryo hatches. The insect starts as a single cell, and then develops into the larval form before it hatches.
The second stage is from birth until the larva pupates. This mobile stage is generally worm-like in form. This worm-like form can be one of several varieties: eruciform (caterpillar-like), scarabaeiform (grub-like), campodeiform (elongated, flattened, and active), elateriform (wireworm-like) or vermiform (maggot-like). This stage usually consists of growth and gaining stored energy for metamorphosis.
The third stage is from pupation until eclosion. This stage is marked by reduced movement and often sealed within a cocoon. There are three types of pupae: obtect, exarate or coarctate. Obtect pupae are compact, with the legs and other appendages enclosed. Exarate pupae have their legs and other appendages free and extended. Coarctate pupae develop inside the larval skin. In this stage, the insect's internals change drastically.
Adult holometabolous insects usually have wings (excepting where secondarily lost) and functioning reproductive organs. In this stage, reproduction is the top priority for Queens and males.
The Orders that contain holometabolous insects are :
- Coleoptera - Beetles
- Diptera - Flies
- Hymenoptera - Ants, bees, sawflies and wasps
- Lepidoptera - Butterflies and moths
- Mecoptera - Scorpionflies
- Megaloptera - Alderflies, dobsonflies and fishflies
- Miomoptera (extinct)
- Neuroptera - Lacewings, antlions, etc.
- Protodiptera (extinct)
- Raphidioptera - Snakeflies
- Siphonaptera - Fleas
- Strepsiptera - Twisted-winged parasites
- Trichoptera - Caddisflies