Parasitism of late instar Culicoides variipennis larvae by the Mermithid nematode, Heleidomermis vivipara, is reported. Parasites were found at 4 geographically distinct sites in central New York State. The nematodes emerged from the host as adults, mated, and the females gave birth to live preparasites. The sex ratio was 41:59 (male:female), with generally either 1 female or 1 or 2 males emerging/host. During the 7-month study at 2 of the sites, average parasitism was 9.8% and 7.1%, but individual collections ranged from 0-54%.