Table of Contents
What is Metamorphosis?
Metamorphosis is the biological process of development of an organism from the time of birth or hatching into an adult stage by abrupt change in the animal’s body such that its mode of nutrition and behaviour, both are changed. It can be seen in fishes, amphibians, crustaceans, molluscs and echinoderms.
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Note: Reptiles do not show metamorphosis. |
Types of Metamorphosis
There are three kinds of metamorphosis: ametabolism, hemimetabolism and holometabolism. All the three kinds can be seen in insects. Let us discuss them one by one.
Ametabolism
It is a type of growth or life cycle in which there is little or no metamorphosis at all. It is observed in primitive wingless insects such as the order Zygentoma and Archaeognatha.
Holometabolism
Holometabolism, also called complete metamorphosis, includes four life stages: egg, larva, pupa and imago. It is commonly seen in insects of order Endopterygota that includes butterflies, bees, ants, flies and beetles. In this developmental life cycle, each stage animal differs from the next stage largely.
Developmental Stages
- Egg: Egg is the first developmental stage of the insect life cycle. The egg is single celled which soon divides to form a larva before hatching. The egg stage is usually very short in insects or can sometimes last for months when the insect goes for hibernation to avoid extreme weather conditions.
Refer: Difference between Diapause And Hibernation
- Larva: Larva is the second stage of holometabolous life cycle. Sometimes, insects lay their eggs on food sources so that the larva can start feeding as soon as the egg hatches. The larva (plu: larvae) has simple eyes rather than compound eyes and possesses no wings or wing buds. Most of the larval stage is worm-like and mobile. On the basis of their body type, the larvae are of four types:
- Elateriform: wireworm-like, e.g., family Elateridae
- Eruciform: caterpillar-like, e.g., order Lepidoptera and Symphyta
- Scarabaeiform: grub-like along with a head capsule, e.g., family Scarabaeidae
- Vermiform: maggot-like, e.g., suborder Brachyceran
- Campodeiform: elongate, flattened with functional legs, e.g., Campodea
- Pupa: The larva undergoes metamorphosis to enter the third developmental stage, i.e., pupa. They are inactive and non-feeding at this stage. Most of the organisms are immobile at this stage but some like mosquitoes are mobile. An organism prepares for pupation by knitting a cocoon made of silk or its own faeces for its protection. After reaching this stage, an organism’s physiology and structure change drastically.
The pupae are of three kinds:
- Obtect: compact, legs and other appendages are closed
- Exarate: legs and other appendages are free and extended
- Coarctate: these pupae develop inside the larval skin
- Imago: Imago, or adult, is the final stage of holometabolous development. They have wings and reproductive organs. The majority of adults do not grow much after eclosion from pupa, some of them don’t feed at all and focus primarily on mating and reproduction while some of them can still divide that is restricted to specific organs.
Hemimetabolism
Hemimetabolism, or incomplete metamorphosis is a type where insects show only three developmental stages: egg, nymph and imago. Organisms undergo gradual changes and there is no pupal stage involved. Nymph, the second developmental stage, has a thin exoskeleton and largely resembles imago but does not have wings or reproductive organs.
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