Insects (frae Laitin insectum, a calque o Greek ἔντομον [éntomon], "cut intae sections") are a cless (Insecta) o hexapod invertebrates within the arthropod phylum that hae a chitinous exoskeleton, a three-pairt bouk (heid, thorax an abdomen), three pairs o jyntit legs, compoond een an ane pair o antennae. Thay are the maist diverse group o ainimals on the planet, includin mair nor a million descrived species an representin mair nor hauf o aw kent leevin organisms. The nummer o extant species is estimatit at atween sax an ten million, an potentially represent ower 90% o the differin ainimal life forms on Yird. Insects mey be foond in nearly aw environs, awtho anerly a smaw nummer o species dwall in the oceans, a habitat dominatit bi anither arthropod group, crustaceans.
The life cycles o insects vary but maist hatch frae eggs. Insect growthe is constrained bi the inelastic exoskeleton an development involves a series o mouts. The immatur stages can differ frae the adults in structur, haibit an habitat, an can include a passive pupal stage in thae groups that unnergae 4-stage metamorphosis (see holometabolism). Insects that unnergae 3-stage metamorphosis lack a pupal stage an adults develop throu a series o nymphal stages. The heicher level relationship o the Hexapoda is unclear. Fossilised insects o enormous size hae been foond frae the Paleozoic Era, includin giant draigonflees wi weengspans o 55 tae 70 cm (22–28 in). The maist diverse insect groups appear tae hae coevolved wi flouerin plants.
Adult insects teepically muive aboot bi walkin, fleein or whiles soummin (see § Locomotion ablo). As it allaes for rapid yet stable muivement, mony insects adopt a tripedal gait in which thay walk wi thair legs titchin the grund in alternatin triangles. Insects are the anerly invertebrates tae hae evolved flicht. Mony insects spend at least pairt o thair leeves unner watter, wi larval adaptations that include gills, an some adult insects are aquatic an hae adaptations for soummin. Some species, such as watter striders, are capable o walkin on the surface o watter. Insects are maistly solitar, but some, such as certain bees, eemocks an termites, are social an leeve in lairge, well-organised colonies. Some insects, such as earwigs, shaw maternal care, guardin thair eggs an young. Insects can communicate wi each ither in a variety o weys. Male mochs can sense the pheromones o female mochs ower great distances. Ither species communicate wi soonds: cheepers stridulate, or rub thair weengs thegither, tae attract a mate an repel ither males. Lampyridae in the clock order communicate wi licht.
Humans regaird certain insects as pests, an attempt tae control them uisin insecticides an a host o ither techniques. Some insects damage crops bi feedin on sap, leafs or fruits. A few parasitic species are pathogenic. Some insects perform complex ecological roles; blaw-flees, for example, help consume carrion but an aa spreid diseases. Insect pollinators are necessar tae the life cycle o mony flouerin plant species on which maist organisms, includin humans, are at least pairtly dependent; withoot them, the terrestrial portion o the biosphere (includin humans) wad be devastatit. Mony ither insects are conseedert ecologically benefeecial as predators an a few provide direct economic benefit. Soiewirms an bees hae been uised extensively bi humans for the production o soie an hinnie, respectively. In some culturs, fowk eat the larvae or adults o certain insects.