Insecta

Insecta is a class within the phylum Arthropoda, consisting of the vast majority of described animal species. Adult insects typically have a three-part body plan (head, thorax, abdomen), one pair of antennae, and six legs. Most possess one or two pairs of wings at some life stage, though many species are wingless. They breathe through a network of tubes called the tracheal system with external openings (spiracles) and have an exoskeleton made of chitin that must be shed during growth. The nervous, digestive, and circulatory systems are adapted to a compact body plan, and many insects rely on highly specialized sensory organs.

Insect diversity is immense, with about 1 million described species and many more likely undiscovered. They occupy virtually every habitat and play essential ecological roles, including pollination, herbivory, predation, decomposition, and serving as a key food source for other animals. Insect life cycles vary; most undergo metamorphosis. Hemimetabolous (incomplete metamorphosis) insects, such as grasshoppers and true bugs, hatch from nymphs resembling smaller adults. Holometabolous (complete metamorphosis) insects, including beetles, butterflies, bees, and flies, have distinct larval and pupal stages that look very different from adults.

Economically and ecologically important, insects can be pollinators of crops, regulate pest populations, or become agricultural pests and disease vectors. They are part of complex ecosystems and have a rich fossil record, illustrating a long and ongoing evolutionary history within the arthropod lineage. Major extant orders include Coleoptera (beetles), Lepidoptera (butterflies and moths), Diptera (flies), Hymenoptera (bees, wasps, ants), Hemiptera (true bugs), Orthoptera (grasshoppers and crickets), and Odonata (dragonflies and damselflies).