The finding of Cnephia ornithophilia Davies, Peterson, & Wood and Prosimulium vernale Shewell for the first time at the Patuxent Wildlife Research Center, Laurel, Maryland, is described. Larvae of C. ornithophilia were collected Nov. 15, pupae Feb. 14, and adult flies Feb. 28. No immature or adult specimens were found between Apr. 2 and Nov. 14. The greatest number of immature stages was found in a 3- to 5-foot-wide stream several hundred feet long, 1-8 inches deep, with a stream flow between 0.49 and 3.30 feet per second. The water temperature varied from 0.5° to 4.0°C, the oxygen content was 10-13 ppm; and the pH varied from 6.9 to 7.4. Larvae of P. vernale were collected Nov. 30 through March, pupae from February through Apr. 1, and adult flies from Feb. 26 through Apr. 1. No immature or adult specimens were found between Apr. 2 and Nov. 29. The largest number of immature stages of P. vernale was found in a 6- to 16-foot-wide stream, 100 feet long, and 1.2 inches deep. The stream flow was between 0.92 and 1.36 feet per second. The water temperature was 0.5°C; pH was 6.7; and oxygen content was 7 ppm.