Background
Clusia is a distinct group of relatively large, showy species more readily recognized on the basis of one pair of interfrontal bristles, a pubescent to short-plumose (not long-plumose) arista, a cloud around crossvein dm-cu (secondarily lost in several species), no preapical tibial bristles, and a scutellum with a central yellow stripe (sometimes expanded to include the entire scutellum).
Clusia (which now includes Paraclusia Czerny and Amuroclusia Mamaev (Lonsdale & Marshall, 2008a)) occurs in the Holarctic and Oriental Regions and is comprised of 13 species. Several are quite commonly encountered in North America and Europe, and consequently, have been discussed at length in the scientific literature over the past 150 years.
 
Characteristics
Clusia species have one pair of interfrontal bristles, two pairs of stout lateral scutellar bristles that greatly exceed the apex of the scutellum (one pair sometimes lost), a pubescent to short-plumose (not long-plumose) arista, a cloud around crossvein dm-cu (secondarily lost in several species), a scutellum with a central yellow stripe (sometimes expanded to include entire scutellum). The male genitalia are characterized by a heavily-sclerotized and anteriorly-produced epiphallus; the female genitalia are characterized by a cylindrical ventral receptacle and dark spermathecae (usually with dark reticulated pattern) that are clear in a small circular region around the point of attachment to the spermathecal duct. 

Relationships
The European Clusia tigrina appears to be the basal lineage of Clusia (ie. the sister group to the rest of the genus), but otherwise the relationships between the species of Clusia are not fully resolved. A revision of the genus is currently being developed. Within the Clusiinae, the following male-specific characters suggest a close relationship between Clusia and the more southern Melanoclusia (Borneo): two rows of posteroventral bristles on the fore and mid femora (also found in the Chilean Clusiidae and Clusiodes), an inner-basal spur on a small, triangular surstylus, a uniquely-shaped pregonite (long, thin, minutely setulose along length and closely-associated with base of phallapodeme) and absence of the lateral lobes of the distiphallus (independently lost in some Sobarocephalinae and most Clusiodinae). The genera Paraclusia Czerny and Amuroclusia Mamaev were recently included as junior synonyms of Clusia by Lonsdale & Marshall (2008a).

Distribution
Clusia is found throughout the Holarctic region, with a single species (C. sexlineata Frey) occurring in the Orient, four species restricted to Japan and three species known only from the Russian Far East. In North America, C. czernyi Johnson and C. lateralis (Walker) are found in the northeast and C. occidentalis Malloch is found along much of the west coast.

Biology
Adults occur on a wide range deciduous tree species (observations on conifers such as pine and spruce are much less frequent), preferring either stumps or dead, bare wood on standing trunks (Roháček1995, Stubbs 1982, personal observations). Stubbs (1982) found adults of C. tigrina most often in August and September on debarked spots on live beech trees. European Clusia have been reared from the stumps of several deciduous species such as beech, birch and elm (Perry & Stubbs 1978, Smith 1950), and have occasionally been reared from conifers (Soós 1981). Smith (1950) collected puparia of Clusia flava in a dry beech stump (10'X2') one inch from the surface in early April (emerged towards the end of the month). North American adults have been reared from poplar and maple logs. Mating pairs are often seen on or under foliage.

North American species:

• Clusia czernyi
• Clusia lateralis
• Clusia occidentalis