ETYM French insecte, Latin insectum, from insectus, p. p. of insecare to cut in. Related to Section. The name was originally given to certain small animals, whose bodies appear cut in, or almost divided. Related to Entomology.
Small air-breathing arthropod.
Any member of the class Insecta among the arthropods or jointed-legged animals. An insect's body is divided into head, thorax, and abdomen. The head bears a pair of feelers or antennae, and attached to the thorax are three pairs of legs and usually two pairs of wings.
The scientific study of insects is termed entomology. More than 1 million species are known, and several thousand new ones are discovered every year. Insects vary in size from 0.02 cm/0.007 in to 35 cm/13.5 in in length.
Throughout their history insects have proved remarkably resilient. Of the insect families alive 100 million years ago in the Cretaceous period, 84% are still living (compared with only 20% for four-legged vertebrate families).
The skeleton is external and is composed of chitin. It is membranous at the joints, but elsewhere is hard. The head is the feeding and sensory center. It bears the antennae, eyes, and mouthparts. By means of the antennae, the insect detects odors and experiences the sense of touch. The eyes include compound eyes and simple eyes (ocelli). Compound eyes are formed of a large number of individual facets or lenses; there are about 4,000 lenses to each compound eye in the housefly. The mouthparts include a labrum, or upper lip; a pair of principal jaws, or mandibles; a pair of accessory jaws, or maxillae; and a labium, or lower lip. These mouthparts are modified in the various insect groups, depending on the diet. The thorax is the locomotory center, and is made up of three segments: the pro-, meso-, and metathorax. Each bears a pair of legs, and, in flying insects, the second and third of these segments also each bear a pair of wings.
Wings are composed of an upper and a lower membrane, and between these two layers they are strengthened by a framework of chitinous tubes known as veins. The abdomen is the metabolic and reproductive center, where digestion, excretion, and the sexual functions take place. In the female, there is very commonly an egg-laying instrument, or ovipositor, and many insects have a pair of tail feelers, or cerci. Most insects breathe by means of fine airtubes called tracheae, which open to the exterior by a pair of breathing pores, or spiracles. Reproduction is by diverse means. In most insects, mating occurs once only, and death soon follows.
Growth and metamorphosis.
When ready to hatch from the egg, the young insect forces its way through the chorion, or eggshell, and growth takes place in cycles that are interrupted by successive molts. After molting, the new cuticle is soft and pliable, and is able to adapt itself to increase in size and change of form.
Most of the lower orders of insects pass through a direct or incomplete metamorphosis. The young closely resemble the parents and are known as nymphs.
The higher groups of insects undergo indirect or complete metamorphosis. They hatch at an earlier stage of growth than nymphs and are termed larvae. The life of the insect is interrupted by a resting pupal stage when no food is taken. During this stage, the larval organs and tissues are transformed into those of the imago, or adult. Before pupating, the insect protects itself by selecting a suitable hiding place, or making a cocoon of some material which will merge in with its surroundings. When an insect is about to emerge from the pupa, or protective sheath, it undergoes its final molt, which consists of shedding the pupal cuticle. Many insects are seen as pests. They may be controlled by chemical insecticides (these may also kill useful insects), by importation of natural predators (that may themselves become pests), or, more recently, by the use of artificially reared sterile insects, either the males only, or in “population flushing” both sexes, so sharply reducing succeeding generations.
The classification of insects is largely based upon characters of the mouthparts, wings, and metamorphosis. Insects are divided into two subclasses (one with two divisions) and 29 orders.
Kukac (vaši, stenice, bube, komarci, muve, zolje, pčele, stršljeni itd.). (lat.)