Insects

Insects or Insecta (from insectum) are  s and the largest group within the. Definitions and vary; usually, insects comprise a class within the Arthropoda. As used here, the term Insecta is with Ectognatha. Insects have a ous, a three-part body (, and ), three pairs of jointed , s and one pair of. Insects are the most diverse group of animals; they include more than a million described and represent more than half of all known living s. The total number of  species is estimated at between six and ten million; potentially over 90% of the animal life forms on Earth are insects. Insects may be found in nearly all, although only a small number of species reside in the oceans, which are dominated by another arthropod group, s.

Nearly all insects hatch from s. Insect growth is constrained by the inelastic and development involves a series of. The immature stages often differ from the adults in structure, habit and habitat, and can include a passive l stage in those groups that undergo. Insects that undergo lack a pupal stage and adults develop through a series of  stages. The higher level relationship of the is unclear. Fossilized insects of enormous size have been found from the Era, including  with wingspans of 55 to 70 cm (22 to 28 in). The most diverse insect groups appear to have with.

Adult insects typically move about by walking, flying, or sometimes swimming. As it allows for rapid yet stable movement, many insects adopt a tripedal gait in which they walk with their legs touching the ground in alternating triangles, composed of the front & rear on one side with the middle on the other side. Insects are the only invertebrates to have evolved flight, and all flying insects derive from one common ancestor. Many insects spend at least part of their lives under water, with adaptations that include s, and some adult insects are aquatic and have adaptations for swimming. Some species, such as, are capable of walking on the surface of water. Insects are mostly solitary, but some, such as certain s, s and s, are social and live in large, well-organized colonies. Some insects, such as s, show maternal care, guarding their eggs and young. Insects can communicate with each other in a variety of ways. Male s can sense the s of female moths over great distances. Other species communicate with sounds:, or rub their wings together, to attract a mate and repel other males. s communicate with light.

Humans regard certain insects as, and attempt to control them using s, and a host of other techniques. Some insects damage crops by feeding on sap, leaves, fruits, or wood. Some species are, and may diseases. Some insects perform complex ecological roles;, for example, help consume but also spread diseases. Insect are essential to the life cycle of many flowering plant species on which most organisms, including humans, are at least partly dependent; without them, the terrestrial portion of the biosphere would be devastated. Many insects are considered ecologically beneficial as predators and a few provide direct economic benefit. s produce and honey bees produce  and both have been domesticated by humans. Insects are consumed as food in 80% of the world's nations, by people in roughly 3000 ethnic groups. Human activities also have effects on.

Phylogenetic tree
From Evolution of insects: