ABSTRACT
Insects are members of the phylum Arthropoda, invertebrate animals characterised by their often hard exoskeleton or body shell, their segmented body and their jointed limbs. Unlike all other arthropods, adult insects usually possess two pairs of wings and three pairs of true legs. The outer skin or integument of an insect is composed of chitin and protein, and is known as the cuticle. This forms a non-cellular, waterproof layer over the body, the precise chemical composition and thickness of which determines its hardness and rigidity. The head of an insect is composed of six fused body segments, and carries a pair of sensory antennae, eyes and mouthparts. The form of an insect antenna varies considerably, the number of so-called antennal ‘segments’ ranging from one to more than a hundred. The body cavity of an insect extends into the appendages, and is filled with a more or less colourless, blood-like fluid called haemolymph.
