Clusiids are characteristically slender acalyptrate flies usually 2.5-6.0 mm in length, most readily identified by an angulate extension on the outer margin of the pedicel, a dorsoapical arista (dorsobasal in other similar families) on an orbicuar first flagllomere, a complete subcosta, one subcostal break (indistinct in most Clusiodinae), one pair of vibrissae, and five or fewer fronto-orbital bristles. Most species are yellow with a brown to black pattern, but several species are predominantly to entirely pale (some Sobarocephala Czerny), and some are predominantly brown to black (many Heteromeringia Czerny and Craspedochaeta Czerny).
There are 3-5 (sometimes 2) fronto-orbital bristles, of which the anterior is sometimes inclinate, and in species with 4-5 bristles the third from the back is sometimes inclinate and proclinate. Interfrontal bristles are convergent or absent. Ocellar and postvertical bristles are either divergent or absent. On the thorax, there are 1-3 dorsocentral bristles, 1 postpronotal, 2 notopleurals, 2-3 intra-alars (the presutural intra-alar is sometimes absent), 1-2 intrapostalars, and 1 strong anepisternal and katepisternal bristle; 1 pair of prescutellar acrostichal bristles sometimes present. Preapical tibial bristles either absent, present on mid tibia only, or present on mid and hind tibiae.
Adults are not often collected, but they can be relatively abundant in some microhabitats. Small dung baits and Malaise traps have been the most successful collection methods , but a number of species have been swept from grass or collected from foliage, logs and dead patches on tree trunks. North American adults appear to prefer mixed and deciduous forests sometimes associated with grass-dominated areas. Tropical species have often been collected along waterways in mossy, humid habitats. Species of Heteromeringia seem to prefer more open forests and have been found in treefalls (Lonsdale & Marshall, 2007a). Clusiids have been known to feed on nectar, rotting vegetative matter, sap (Soós, 1987), and the dung of birds and mammals.
Clusiidae are among the few acalyptrates that form leks. Males establish dominance at a lek site, defending mating territories (devoid of resources) from other males. True lekking behaviour has only been seen in the subfamily Clusiodinae so far (see photos of Craspedochaeta pullipleura Lonsdale & Marshall from Bolivia), but indirect evidence, such as antlers in Procerosoma Lonsdale & Marshall and widened heads in Sobarocephala, suggest that similar male agonistic behaviour is more widespread in the family.
After mating, the females lay eggs elsewhere, usually under bark or in wood in a state of more advanced decay than the dry surface used for lekking (Roháček, 1995). Selection of clusiid oviposition sites does not appear to be associated with any particular species of tree, but is limited by "humidity, amount of shade, stage of wood decay, [and the] presence of mycelia of certain fungi" (Roháček, 1995). Rearing records suggest that most temperate species can be found in a number of different deciduous trees, but some Clusiodes have also been found in conifers (Roháček, 1995) and larvae of Sobarocephala have been found termite colonies as well as decaying wood (Sóos, 1987). Malloch (1918) found the larvae of S. flaviseta to be "evidently associated with the burrows of coleopterous insects" and to be relatively sluggish and slow moving. Clusiid larvae are probably at least facultatively predaceous on larvae of other wood-boring insects.
As discussed above, males of some clusiids, particularly Hendelia Czerny, have enlarged heads or other conspicuous modifications used in fighting or mutual assessment on lek sites (McAlpine, 1976; Marshall, 2000). Sobarocephala latipennis Melander & Argo and several Australian Hendelia have strongly widened heads, and Hendelia kinetrolicros (Caloren & Marshall), Hendelia mirabilis (Frey), and Procerosoma alini (Shatalkin) have spectacular long genal processes that are probably used in male-male agonistic interactions, although these species have never been observed while engaged in such behaviour. Analogues of the widened head can be seen in the North American species Heteromeringia nitida, which holds its contrastingly coloured fore legs out to the side of the head and folds its tibiae backwards, using these bent legs to exaggerate body size.