Overview

Adults are most often found on or near shrubs infested by mealy bugs of the family Margarodidae, and the larvae are endoparasites of these insects. Some species of Cryptochetum have been used for biological control of margarodids. Librella has been collected in eucalypt forest, but it biology is unknown.

Description

Typical cryptochetids (genus Cryptochetum) are very small, rotund, blackish flies with the following features:
Bristles of head and thorax mostly not differentiated from the numerous setulae; face sclerotised; first flagellomere of antenna large, elongate and drooping; arista minute or absent; scutellum setulose, but with at most very short bristles; prosternum broad, with precoxal bridge; legs without differentiated bristles; wing broad; vein C with subcostal break, but humeral break less obvious or absent; vein Sc very incomplete; cells bm and dm confluent; cell cup partly enclosed, but open on posterior side; vein A1+CuA2 very long, reaching wing margin or almost so.

The position of Librella in this family is uncertain. It differs from Cryptochetum by possessing the following features:

General coloration tawny; antenna with long arista; head and thorax with numerous differentiated bristles, including convergent postocellars, but vibrissa and anepisternal bristle absent; vein A1+CuA2 relatively short.

Distribution

Most Cryptochetum species live in Africa, East Asia and Australia, but at least one species has been introduced to North America. In Australia, there are four species. The genus Librella has only been found in the Australian Capital Territory and New South Wales and the male is still unknown. It is rather similar to the fossil genus Phanerochaetum known from Baltic Amber in the early Tertiary.