Insects generally undergo metamorphosis to reach adulthood. Metamorphosis is defined as a biological process in which the animal undergoes physical development after its birth. The body structure of the animal changes vastly through cell growth and differentiation.
The Larva is the young form of many animals before they undergo metamorphosis to grow into adults. This is a kind of indirect development in many animals which include amphibians, insects, etc. All these animals have typically a larval stage in their lifecycle. The appearance of the Larva is very distinctive when compared to that of their adult form. The Larval stage of an insect general includes many structures that are not found in their adult form. The environment adaptability, as well as their food and diet, also is completely different than that of the adult version of the animal.
The larval population of a given amphibian or an insect has more susceptibility to survive from predators when compared to that of their adult population due to their distinctive environment where they live. For example, the larval stage of a frog is a Tadpole that lives exclusively in water and cannot survive outside the aquatic environment unless and until it reaches the adult stage which is called a frog that can live on both land and water.
While some larvae are capable of surviving alone until they mature into adults, there are some larvae that need the help of the adults to be fed. These include the Hymenoptera species in which the female adults are responsible for providing food to the larva.
(Image to be added soon)
The pupal stage comes after the Larval stage. The lifecycle of an insect undergoes 4 different stages which are egg, larva, pupa, and imago (adult stage) respectively. The pupal stage of an insect is controlled and regulated by the hormones of the insect, unlike the larval stage. The stage where the Larva becomes the Pupa is called the Pupation. The cells present in the larval stage start growing rapidly. They then become various organs of the insect-like the eyes, wings, legs, etc of the insect. Every variety of insects has a different name for their pupa. For example, the pupae of the butterflies are called the chrysalis. Usually, the pupae are enclosed within a cavity called the shells or cocoons.
In an Exarate pupa, the appendages are free whereas
In an Obtect pupa, the appendages are very much attached to the body wall like the cocoon.
Again based on the mandibles the pupa can be classified under two varieties:
Adecticous pupa where the pupae are without the articulated mandibles.
Decticous pupa where pupae are with articulated mandibles.
Generally. The pupae are immobile and hence do not have much defence mechanism to defend themselves from the predators. That is when their external covering comes to their rescue. Either the pupa is covered with the shell or cocoon or they conceal themselves from the environment by going underground. In some varieties, the pupae are protected by other insects whereas a few varieties of pupae secrete toxic substances to protect them from becoming a meal of the predators.
Depending upon different varieties of the insects, the pupal stage may last up to a week or even years before they reach adulthood.
(Image to be added soon)
The insects and a few amphibians undergo the lifecycle which includes the larval stage and pupal stage but the appearance and duration in each case are different than the other.
1. What is complete metamorphosis?
A metamorphosis is termed when the insect undergoes different stages of the life cycle starting from the egg, larva, pupa, and then adult respectively. In complete metamorphosis, the adult stage looks completely different from the larval stage. In every stage, the appearance of the insect changes drastically.
Similarly, not every insect or an amphibian undergoes complete metamorphosis. There are a few varieties of insects where the appearance of the newly hatched insect from the egg looks quite similar to the adult version. These particular juvenile forms are called the Nymphs. Nymphs shed their exoskeleton until they grow and reach their adult size. A few examples include the dragonflies and grasshoppers which undergo incomplete metamorphosis.
2. What is a cocoon?
A cocoon is a protective covering for a pupa spun out of silk secreted by many caterpillars and moths. Depending on the type of insect, the cocoon can be soft or hard, translucent or opaque, and of various colours. The pupae that lie inside the cocoon either cut their way out or secrete some enzymes that soften the cocoon thus helping the insect come out of the cocoon as an adult.