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| Arthropoda :: insects :. Anatomy. Insect parts
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Insects are incredibly diverse. They range in size from 0.1 mm to 30 cm in length or wingspan. In North America the largest insects are the moths with a wingspan of up to 15 cm and stick insects with a body length of 15 cm. Insects range in colour. They can be drab, brilliant, glittery, or iridescent.
The Head
Insects' bodies are composed of three sections: the head, thorax and abdomen. The head contains one pair of antennae, the eyes and the mouthparts. Most insects have compound eyes. The mouthparts of insects are elaborate and vary widely in relation to feeding habits. Some insects such as beetles, ants and grasshoppers have chewing or mandibulate mouthparts. Others, like aphids, have mouthparts that are specialized for sucking, piercing, or absorbing liquids.
The Thorax
The thorax consists of three segments or tagmata, each with a pair of legs. The legs however, are completely absent in the larvae or young, of certain groups. Insects may have no wings or one or two pairs. If the insect has two pairs of wings then they are attached to the middle and hind segments of the thorax. If there is only one pair of wings they are usually attached to the middle segment. The thorax is almost entirely filled with muscle that operates the legs and wings. The wings are one feature that has enabled insects to colonize many areas. They can fly away from a habitat when it becomes unsuitable or simply exploit new places.
The Abdomen
The abdomen does not have any locomotor appendages, but may have some special appendages on the end of it. The abdomen is typically segmented into eleven parts, the maximum visible number being 10. Segments 8 and 9 are the genital segments. In male insects these segments bear structures that are associated with copulation and the transfer of sperm to the females. In females these segments have appendages which form the ovipositor. An important feature for identification are the cerci at end of the abdomen. They are appendages which arise from segment 10 and may be clasper-like, feeler-like or absent.
The Exoskeleton
Insects have a tough outer covering, the exoskeleton, against which the muscles work. The principal structural element in this external skeleton is chitin, a modified form of cellulose. It is secreted by the epidermis and varies greatly in toughness and thickness in different insects. It prevents water loss and helps to protect the insects from predators, parasites and injury. Young insects shed this outer layer a number of times in a process of molting or ecdysis, before they become adults. Once they are adults, this molting stops permanently. When they outgrow their exoskeletons they form a new one underneath the old. Insects molt 4-8 times during the course of development and some species as many as 30 times. The stages between the molts are called instars. When an insect first emerges following ecdysis, it is usually pale, soft and susceptible to predators. The exoskeleton hardens in an hour or two. |
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