General & Distribution
Clusia occidentalis,
the only species of Clusia in western North America, is found along the west coast from the northern part of California's central coast bioregion to Prince Rupert, British Columbia (just below the Alaskan panhandle). More focused collecting, however, may extend the range of this species further south and into the Hemlock-dominated portion of the boreal forest.

Similar species
Clusia occidentalis is a very large (approx. 5mm), skinny, pale species, easily-separated from other western flies. The pleuron, notum, legs, abdomen and head are almost entirely light yellow, although some specimens have one pair of faded lateral stripes on the face (the eastern species of Clusia have entirely dark or strongly-vittate faces). This species is also characterized by a dark C-shaped marking on the wing, which is also found in C. czernyi.