The Sooty Hairstreak (Satyrium fuliginosum) is a butterfly of the Lycaenidae family. It is found in western North America from British Columbia to central California, east to Wyoming and northern Colorado. The wingspan is 24–30 mm. The upperside is drab dark grey. The underside is grey to greyish brown. The forewing sometimes has a line of white-bordered dark spots. Adults are on wing from July to August. Adults feed on flower nectar. The larvae feed on Lupinus.