Insects are invertebrates of the class Insecta and the largest group within the arthropod phylum. The cited article says insects have an exoskeleton, a three-part body of head, thorax and abdomen, three pairs of jointed legs, compound eyes and a pair of antennae, that they are the most diverse group of animals, with more than a million described species representing more than half of all animal species, and that the insect nervous system consists of a brain and a ventral nerve cord. It is the insect half of the combined insect or mite value. Pests and diseases recorded in the atlas as caused by an insect are grouped under this concept.