Class Insecta: Structure, Life Cycle, and Physiology
General Characteristics of Insects
- Insects belong to the phylum Arthropoda and are among the most diverse organisms on Earth.
- Their bodies are divided into three major segments: the head, the thorax, and the abdomen.
- They possess three pairs of walking legs, making a total of six legs.
- Most insects have two pairs of wings, which are extensions of the body wall.
- The head typically contains a pair of large compound eyes and three smaller simple eyes called ocelli.
- A pair of antennae is present on the head, used for sensing the environment.
Development and Metamorphosis
Insects grow through various types of metamorphosis, which refers to their transformation during development:
- Ametabolous development:
- Young insects resemble miniature adults.
- They grow through a process of molting (ecdysis) but do not undergo dramatic changes in form.
- Hemimetabolous development:
- The immature stages are called nymphs.
- Nymphs look like small, wingless versions of adults and gradually acquire adult features through multiple molts.
- Examples include lice and bedbugs.
- Holometabolous development:
- This form of development occurs in nearly ninety percent of insect species.
- The young hatch as larvae, which look entirely different from the adults and often live in different habitats.
- After feeding and growing, the larva forms a pupa inside a protective casing.
- The adult emerges after significant internal transformation.
- Examples include fleas.