There are about one million species of insects, and many more to be discovered. They include, for example, ants, bees, wasps, beetles, butterflies, dragonflies and fleas. They range in size from microscopic soil inhabitants to large beetles and butterflies, but they all share some common characteristics.
Their bodies are divided into about 20 parts, divided into the head [6 fusion parts], the chest [3 parts] and the abdomen [11 parts]. All insects have an exoskeleton consisting of a hard cuticle.
There are sensory organs and mouthparts on the head. There is a pair of antennas that are sensitive to touch and smell. There is also a pair of compound eyes, composed of hundreds of independent lenses and sensory cells. They can detect light, motion and color, and can form rough shape images. In bees and butterflies, these senses enable insects to find the source of nectar in the flower by color, shape and smell.
There are three sets of mouthparts on the outside of the head. A pair of chins [squats] bite off a portion of the food and pass them through the mouth. A pair of upper jaws helps to taste and manipulate food and the labia [lower lip '] has multiple functions depending on the type of insect.
All insects have three pairs of legs, one for each chest segment. Each leg has five sections with joints between each section that allow the legs to move in different directions. The exoskeleton at the joint consists of a pliable cuticle that is free to move.
Also typically has a pair of wings on each of the second and third segments of the chest, but in some insects [e.g., flies and mosquitoes] these can be reduced to a pair, and many species have no wings at all.
In mature insects, the abdomen has no appendages other than the devices on the last segment to help lay eggs.
The sturdy exoskeleton supports the insect, retains its shape and protects it from damage and evaporation. A hard exoskeleton prevents insects from growing in a continuous manner and growth occurs in the spray. The stratum corneum of the outer layer falls off and the insect expands its body until a new stratum corneum forms and hardens. This molting process [or molting] occurs 5 or more times until mature insects appear, after which no further growth or molting occurs.
Intermittent growth occurs during the larval or nymphal phase of the insect's life cycle. Insects such as butterflies or bees that exhibit complete metamorphosis have larval stages that are completely different from adults, such as maggots or butterfly caterpillars. The penultimate moulting results in a stationary phase, ie sputum, in which adult features are formed. The last moulting reveals mature insects.
In insects such as ticks or mites with incomplete metamorphosis, the early stages are called nymphs, which are very similar to adults, except that their wings are not formed. Minor morphological changes occur every time the molting occurs until mature winged insects appear.
Orignal From: Biology - Characteristics of Insects - Introduction
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