Difference Between Molting and Metamorphosis

Main Difference – Molting vs Metamorphosis

Molting and metamorphosis are two events of the life cycle of animals. The main difference between molting and metamorphosis is that molting refers to the shed of body parts periodically such as body coverings, feathers, cuticles or skin whereas metamorphosis refers to the process of transformation from an immature form to the mature form through distinct stages. Molting mainly referred to the shed of the exoskeleton of arthropods. Metamorphosis occurs in insects and all animals. The two main types of metamorphosis are incomplete metamorphosis and complete metamorphosis.

Key Areas Covered

1. What is Molting
     – Definition, Process, Examples
2. What is Metamorphosis
     – Definition, Stages, Examples
3. What are the Similarities Between Molting and Metamorphosis
     – Outline of Common Features
4. What is the Difference Between Molting and Metamorphosis
     – Comparison of Key Differences

Key Terms: Adult, Complete Metamorphosis, Ecdysis Egg, Exoskeleton, Incomplete Metamorphosis, Molting, Nymph

What is Molting

Molting refers to the shed of outer body covering, feathers, hair or skin to make way for new growth. Both animals and arthropods regenerate their external tissues during their life cycle. In arthropods, the body is covered with a thick or thin exoskeleton that is not detached progressively. This restricts the growth of the arthropod, becoming a barrier to increase the size of the body. Thus, the exoskeleton should be shed to achieve further growth. This type of molting is referred to as ecdysis. Ecdysis occurs in nematodes as well. Ecdysis of a cicada is shown in figure 1.

Figure 1: Ecdysis

Molting is also involved in the shedding of the epidermis and pelage (hair, feathers, fur etc.). Amphibians, snakes, and lizards shed their skin. Birds shed their feathers periodically. Dogs and cats shed their fur. Molting helps in adapting different environmental changes in animals such as birds.

What is Metamorphosis

Metamorphosis refers to the process of transformation from an immature form to an adult form through distinct life stages. Both body form and the habitat may change during metamorphosis. Metamorphosis occurs in cnidarians, insects, crustaceans, mollusks, and animals such as fish, amphibians, echinoderms and all chordates. Based on the stages of each life cycle, two types of metamorphosis can be identified.

Complete Metamorphosis

Complete metamorphosis includes egg, larva, pupal, and adult stages, which differ greatly in morphology. The lifecycle of butterflies, ants, fleas, bees, beetles, moths, and wasps are examples of complete metamorphosis.  Complete metamorphosis starts with the laying of eggs by the female insect. The larva,  the second stage of complete metamorphosis, are hatched from eggs. The larval stage is typically different from the adult stage in morphology, behavior, and/or habitat. The larval body is soft and worm-like. The life stages of a butterfly are shown in figure 2.

Figure 1: Life Stages of a Butterfly

Ravenous feeding of the larva is their most significant feature. Due to this great appetite for food, this stage shows very fast growth. Larva molts their skin several times during this growth. The pupal stage begins with the formation of cocoons around the larvae. The larva is inactive and does not feed when they are inside the cocoons. Their bodies develop more segments, internal organs, legs, and wings. The pupal stage may exist from 4 days to several months. A fully developed adult is finally freed from the cocoon.

Incomplete Metamorphosis

Incomplete metamorphosis is a development where gradual changes occur in the insect during the development from the egg to the adult. Egg, nymph, and adult are the three stages of the incomplete metamorphosis. The eggs are laid by the female insect. In most cases, the eggs are covered by an egg case, which protects and hold the eggs together. The eggs hatch into younger nymphs. The life stages of a grasshopper are shown in figure 3.

Figure 3: Life Stages of a Grass Hopper

The nymph resembles the adult without wings. The nymph is also smaller than the adult. The nymph eats the same food as the adult. It develops into the adult through a series of molts. It shed its exoskeleton 4-8 times. When it becomes an adult, molting does not occur.  Incomplete metamorphosis can be seen in termites, lice, true bugs, grasshoppers, praying mantis, crickets, and cockroaches.

Similarities Between Molting and Metamorphosis

• Molting and metamorphosis are two types of events of the lifecycle of animals.
• Both molting and metamorphosis are structural changes of the body.
• Both molting and metamorphosis bring the nymph to an adult.

Difference Between Molting and Metamorphosis

Definition

Molting: Molting refers to the shed of outer body covering, feathers, hair or skin to make way for a new growth.

Metamorphosis: Metamorphosis refers to the process of transformation from an immature form to an adult form through distinct life stages.

Occurrence

Molting: Molting occurs in arthropods, amphibians, reptiles, and birds.

Metamorphosis: Metamorphosis occurs in cnidarians, insects, crustaceans, mollusks, and animals such as fish, amphibians, echinoderms and all chordates.

Types

Molting: Molting mainly refers to the shed of the exoskeleton in insects.

Metamorphosis: Incomplete metamorphosis and complete metamorphosis are the two types of metamorphosis.

Role

Molting: Molting helps animals to increase the size of the body.

Metamorphosis: Metamorphosis helps to transfer from one life stage to the next.

Conclusion

Molting and metamorphosis are two types of events in the lifecycle of animals. Molting mainly refers to the shed of the exoskeleton in arthropods. Metamorphosis is the transformation process of the animals from an immature form to a mature form. The main difference between molting and metamorphosis is the type of process in the above-mentioned events.

Reference:

1. “Metamorphosis.” Arthropod Morphology, Available here.
2. “Molt.” Encyclopædia Britannica, Encyclopædia Britannica, inc., 20 Sept. 2017, Available here.

Image Courtesy:

 1. “Ecdise” By Macau500 – Own work (Public Domain) via Commons Wikimedia
2. “Papilio demoleus 1600X1200” By Original uploader was Neo gfx at en.wikipedia – Transferred from en.wikipedia, (CC BY-SA 3.0) via Commons Wikimedia
3. “Grasshoppermetasnodgrass” By S.E. Snodgrass – Fig. 9 from Insects, their way and means of living, R. E. Snodgrass. Archive.org (Public Domain) via Commons Wikimedia