Like all scale insects, diaspidids are strongly sexually dimorphic. Adult females are typical of the Coccoidea in being larviform, but can be distinguished from those of other families by: legs absent; antennae reduced to stumps, lacking articulation; abdominal segments IV-VIII fused into a sclerotized pygidium; and by secretion of a separate, non-living scale cover incorporating the shed cuticles (exuviae) of previous instars. The anus is situated on the dorsum and never has any hinged structure associated with it. The pygidium bears a complex of specialized structures (tubular ducts, marginal lobes and plates or gland spines) for the formation of the scale cover.
The scale cover is formed of fibrous secretions of the pygidial ducts, the exuviae of previous instars and anal excreta. Protective scale covers are secreted by the immature stages of both sexes and the adult females, each successive stage enlarging and strengthening the cover made by the previous one, and incorporating the exuviae of the previous stage. In some species the adult female never emerges from the exuviae of the second instar (pupillarial species).
Adult male diaspidids differ from other male Coccoidea in lacking an obvious constriction between the head and prothorax, and in the detailed structure of the thorax; they also have very long genitalia. Otherwise they are typical male scale insects, short-lived and lacking mouthparts, with well-developed antennae and legs, forewings usually present, several pairs of simple eyes, and hind-wings reduced to hamulohalteres. Structurally, males are much more complex than females and provide many more characters for phylogenetic analysis. In some species, both winged and wingless males can occur.
Reproduction in the Diaspididae is usually sexual but parthenogenesis occurs in some species (various authors in Rosen, 1990). Ovipary, ovovivipary and vivipary occur in different species; the eggs lack a peduncle and are laid under the protective scale cover. There are two immature stages in the female and four in the male. The first instar (crawler) possesses legs and is the main dispersal stage, as all subsequent stages of the female are legless.
The general morphology of the adult female is discussed in the Introduction module.