The changes in form that occur as an insect approaches adulthood. When the immature insects and the adults are similar in appearance, the process is called simple metamorphosis, and the juvenile insects are called nymphs. When the immature insects and the adults have different forms, the process is called complete metamorphosis, and the worm, or grub, like juvenile insects are called larvae. After the last larval instar, the insect changes into a pupa. In this stage, the insect does not feed or move around much. It may be covered by a protective cocoon. Eventually the insect molts for the last time and emerges as an adult
Two types of metamorphosis are shown. In a complete metamorphosis (holometabolous) the insect passes through four distinct phases which produce an adult that does not resemble the larvae. In an incomplete metamorphosis (hemimetabolous) an insect does not go through a full transformation, but instead transitions from a nymph to an adult by molting its exoskeleton as it grows.
The immature insects and the adults have different forms, often live in different habitats, and may have very different behavior.
Egg: Most insects lay eggs in a location that offers some protection and food for the newly hatched juveniles. Many eggs are spherical, oval, or elongate, and some have elaborate sculptured shells.
Nymph: The immature form of insects with simple metamorphosis. (Stages between molts of the exoskeleton are called instars).
Larva: The immature form (between egg and pupa) of insects with complete metamorphosis. (Stages between molts of the exoskeleton are called instars)
Pupa: When insects undergo complete metamorphosis, this is the form in between the last larval instar and the adult. In this stage, the insect does not usually feed or move around much. It may be covered by a protective cocoon.
Types of Larvae:
Most insect field guides provide information to help you identify adult insects. Whether you are a dedicated insect enthusiast or a gardener trying to control a plant pest, you may need to identify immature insects from time to time.
About 75% of insects undergo a complete metamorphosis with a larval stage. In this stage, the insect feeds and grows, usually molting several times before reaching the pupal stage. The larva looks quite different from the adult it will eventually become. Identifying insect larvae can be challenging. Your first step should be determining the larval form. Entomologists describe 5 types of larvae, based on their body shape, as follows.
Eruciform Larvae :
Eruciform larvae look like caterpillars (and in most cases, are caterpillars). The body is cylindrical in shape, with a well-developed head capsule and very short antennae. Eruciform larvae have both thoracic (true) legs and abdominal prolegs. Eruciform larvae may be found in the following insect groups:Lepidoptera , Mecoptera, Coleoptera, Hymenoptera (Symphyta)
Scarabaeiform larvae are commonly called grubs. These larvae will usually be curved or C-shaped, and sometimes hairy, with a well-developed head capsule. They bear thoracic legs, but lack abdominal prolegs. Grubs tend to be slow or sluggish. Scarabaeiform larvae are found in some families of Coleoptera (specifically, those classified in the superfamily Scarabaeoidea).
Campodeiform larvae are usually predaceous and typically quite active. Their bodies are elongate but slightly flattened, with well-developed legs, antennae, and cerci. The mouthparts face forward, helpful when they are in pursuit of prey.Campodeiform larvae may be found in the following insect groups:Coleoptera ,Trichoptera, Neuroptera etc
Elateriform larvae are primarily found in Coleoptera, specifically the Elateridae for which the form is named.
Vermiform larvae are maggot-like, with elongate bodies but no legs. They may or may not have well-developed head capsules.
Vermiform larvae may be found in the following insect groups:
Diptera, Siphonaptera, Hymenoptera, Orthoptera, Lepidoptera, Coleoptera etc.
Types of PupaE
The pupal stage of an insect's life is both mysterious and miraculous. What appears to be a motionless, nearly lifeless form is actually an insect undergoing a remarkable transformation. Although you can't see what occurs within a cocoon, you can understand a bit more about the process of metamorphosis by learning the differences between pupal forms.
Only insects that undergo complete metamorphosis have a pupal stage. We use