Spring emergence patterns of tree hole Culicoides were examined at 11 geographic locations. Habitat selection was one mechanism of partitioning used by Culicoides. One group (3 species) occupied tree holes with standing water (wet), while the other (7 species) inhabited tree holes without standing water (dry). The wet tree hole species had sustained emergence patterns, emergence maintained over several consecutive weeks. The dry tree hole species had phasic or biphasic emergence lasting fewer days or occurring as 2 short periods. In both dry and wet habitats, species emerged in a temporal sequence. This temporal sequence was disrupted if a species occupied a type of tree hole (wet/dry) from which it did not normally occur.