Culex nigripalpus is a medium-sized mosquito. The proboscis is dark and the palpi short. The scutum is brown with fine dark bronze to brown scales. The pleura has few or no scales. Abdominal tergites are covered with dark-brown to black scales with bronze to metallic blue-green reflection. Narrow white basal bands are occasionally present on the dorsal surface of some abdominal segments. Legs are dark with reflective bronze to metallic blue-green scales. The posterior surface of the femora and tibiae are pale. In general, this is a dark brown, nondescript species with no obvious distinguishing characteristics, making field identification to the species level extremely difficult.
Wings long and narrow, with scales along the veins. Bodies also very thin. Females bite, but males do not; the female proboscis has 6 piercing parts. Body length: To 3/4″.