Jaws under Hexapoda); in the presence of a large number of excretory (Malpighian) tubes; in the firm texture of the forewings; in the presence of appendages (cerci) on the tenth abdominal segment; and in the absence of a metamorphosis, the young insect after hatching closely resembling the parent.
The insects comprised in it are distinguished from the earwigs by their elongate, rather narrow forewings, which usually cover, or nearly cover, the abdomen when at rest, and which are firmer in texture than the hindwings.
The hindwings have a firm costal area, and a more delicate anal area which folds fanwise, so that they are completely covered by the forewings when the insect rests.
In the Mesozoic rocks (Trias and Lias) there have been discovered remains of insects intermediate between those ancient forms and our modern cockroaches, the differentiation between forewings and hindwings having begun.
The Cimicidae have the feet three-segmented and the forewings greatly reduced; most of the species are parasites on birds and bats, but one - Cimex lectularius (figs.