Body usually globular, frequently occurring in thick test; white tube usually protruding from posterior apex of test; most instars with reduced cone-shaped legs, but Coelostomidia and Mimosicerya with fully developed legs.
This subfamily is highly variable morphologically but seems to form a discrete group of 5 genera. Coelostomidiidae Morrison was first used as a family by Koteja (1974).
Coelostomidiids occur in New Zealand, Mexico, and Central and South America.
Coelostomidiids occur on a wide array of hosts, but generally are found on trees or shrubs.
Coelostomidiids have 4 instars in the female and 5 in the male. The biology of some New Zealand species has been studied in detail. An example of a typical coelostomidiid life cycle is of Ultracoelostoma assimile: Crawlers emerge from the test through the anal tube exit hole; they settle in crevices on the bark, begin feeding, develop the anal wax tube, and become enveloped in a fluffy wax covering that eventually hardens. The remaining 3 instars reside in the test and the shed skins of each are pushed to the posterior end of the test. Second and third instars have reduced conical legs and continue to feed and enlarge the test. Adult females have reduced mouthparts and do not feed. Eggs are laid as the female shrivels and eventually fill the test. The first two instars of the male are identical to those of the female. The third instar is the prepupa and it apparently emerges from the test through the anal tube exit hole. This instar is quite active and moves to the base of the host tree. The fourth instar is the pupa and it molts to the adult inside a white fluffy cocoon.