Scientists employ a system of biological classification, known as taxonomy, to organize and understand this vast array of organisms. This systematic arrangement helps researchers categorize living things based on shared characteristics and evolutionary relationships. By placing organisms into increasingly specific groups, this hierarchical system clarifies where different life forms, including insects, fit.
The Animal Kingdom
All insects belong to the Kingdom Animalia. Organisms within this kingdom share several fundamental characteristics that set them apart from other forms of life. Animals are multicellular organisms, composed of numerous specialized cells.
They are eukaryotic, indicating their cells possess a true nucleus and other membrane-bound organelles. Animals are also heterotrophic, which means they obtain nutrients by consuming other organisms, as they cannot produce their own food. Most animals are motile, capable of movement at some stage of their life cycle, and their cells notably lack rigid cell walls, unlike plants.
The Arthropod Phylum
Within the expansive Kingdom Animalia, insects are further categorized into the Phylum Arthropoda, a group renowned for its immense diversity. This phylum encompasses a vast array of invertebrates, including crustaceans, arachnids, and myriapods, alongside insects. Arthropods are distinguished by an external skeleton, segmented bodies, and jointed appendages. This tough outer covering, called an exoskeleton, is made primarily of chitin and provides support and protection to the animal. The presence of jointed legs, from which the phylum gets its name (“arthro” meaning joint and “poda” meaning foot), allows for varied forms of movement and specialized functions.
Defining Insects
Insects are classified under the Class Insecta, a distinct group within the Phylum Arthropoda. While all insects are arthropods, specific features define them and set them apart from other arthropod groups. Their body is distinctly divided into three main segments: a head, a thorax, and an abdomen.
The head bears sensory organs like antennae and compound eyes. The thorax is the middle segment, and it is to this region that three pairs of jointed legs are attached, giving insects their characteristic six-legged appearance. Many insect species also possess one or two pairs of wings, which are found on the thorax, making them the only arthropods capable of true flight. The abdomen, the posterior segment, houses most of the digestive, excretory, and reproductive organs. These specific anatomical differentiations collectively distinguish insects from other arthropods.