Arthropoda

Insects are the most diverse group of animals in the world. They are members of the phylum Arthropoda and are identified by three pairs of jointed legs, three body segments, an exoskeleton, one pair of antennae, and usually two pairs of wings. Due to the marked diversity of insects, this chapter primarily uses honeybees for descriptions of anatomy and histology; comparisons to specific groups are provided when necessary. As in all arthropods, the alimentary tract can be divided into the foregut, midgut, and hindgut. The primary excretory system is the Malpighian tubules, which are blind-ended, tubular diverticula that branch from the terminal portion of the midgut. As with all other arthropods, the circulatory system includes the heart, aorta, sinuses, and hemolymph. The primary immune cells of insects are hemocytes. The tracheal system is essentially an invagination from the body wall, and as a result is lined internally by cuticle.