Metamorphosis in insects - SS2 Biology Lesson Note

Metamorphosis is a biological process by which an organism undergoes a distinct and often dramatic change in its body structure and physiology as it progresses through different stages of its life cycle. This process typically involves a series of developmental stages, each with its unique characteristics and ecological adaptations. Metamorphosis is commonly observed in various animal groups, including insects, amphibians, and some marine invertebrates.

There are two primary types of metamorphosis: incomplete metamorphosis (hemimetabolous) and complete metamorphosis (holometabolous). Let's explore each type:

1.       Incomplete Metamorphosis (Hemimetabolous): Incomplete metamorphosis is characterized by three distinct stages: egg, nymph, and adult. In this type, the young, called nymphs, resemble miniature versions of the adults but lack certain features, such as functional wings or reproductive organs. The nymphs undergo a series of molts or shedding of their exoskeletons as they grow, gradually developing into adults. However, they do not undergo a drastic restructuring of their body plan during this process. An example of an organism that undergoes incomplete metamorphosis is a grasshopper. The grasshopper's life cycle begins with the laying of eggs. After hatching, the nymphs emerge and resemble miniature grasshoppers. The nymphs gradually grow, shedding their exoskeletons and developing wings and reproductive organs. Eventually, they reach the adult stage.

 

2.       Complete Metamorphosis (Holometabolous): Complete metamorphosis involves four distinct stages: egg, larva, pupa, and adult. Each stage of development is morphologically different from the others, and there is a dramatic restructuring of the organism's body during the transition from one stage to the next.

a.       Larva: The larval stage, also known as the caterpillar or grub stage, is the feeding and growth stage. Larvae often have distinct body structures, specialized mouthparts, and may have different lifestyles or habitats than the adult form. Larvae typically consume large amounts of food to support rapid growth.

b.       Pupa: The pupal stage is a transitional stage during which the larva undergoes a process called metamorphosis within a protective structure called a pupa or chrysalis. Inside the pupa, the larval tissues are broken down and reorganized into the adult body structure. This restructuring involves the development of adult appendages, organs, and external features.

c.       Adult: Once metamorphosis is complete, the adult emerges from the pupal case. The adult stage is the reproductive and usually the mobile stage of the organism. Adults often have distinct body shapes, specialized sensory organs, and reproductive structures necessary for mating and reproduction.

 

An example of an organism that undergoes complete metamorphosis is a butterfly. The butterfly's life cycle starts with the laying of eggs. The eggs hatch into caterpillars, which are the larval stage. The caterpillar feeds, grows, and eventually forms a pupa or chrysalis. Inside the pupa, the caterpillar undergoes dramatic changes and transforms into a butterfly. The adult butterfly emerges from the pupa and is ready for reproduction.