Adult female Culicoides occidentalis Wirth and Jones were collected in a coastal salt marsh habitat in southern California over a period of 15 mo using CO₂-baited suction traps. Adults were active year-round. Adult females overall were large based on wing length (1.86 mm). Because of coastal influences, daily and seasonal changes in air temperatures were greatly buffered, and mean temperatures ranged from 10 to 15°C in winter to 19–21°C in summer. Wing lengths varied inversely with air temperatures, with an average of 2.13 mm (February) to 1.6 mm (July). Parity was consistently low (3.6% overall) and may reflect poor host availability in this isolated salt marsh habitat.