Sicus ferrugineus is a species of fly from the genus Sicus in the family Conopidae. It is common throughout much of Europe. The body is mainly reddish-brown or yellow-brown. The head is yellow, quite large and inflated-looking, with a kind of bubble at the front, narrow cheeks and short antennae. The large eyes are reddish. When in resting position the abdomen is usually folded forward. Their larvae are endoparasites of bumble bees of the genus Bombus (B. lapidarius, B. terrestris, B. hortorum, B. pascuorum, etc.). They pupate and overwinter in their victims.