Males and females have white spots on the forewing, including a white spot in the forewing cell (the oval space between veins that is toward the leading edge of the forewing, near the body); white spots are larger on females. Overall color is brown without a hint of gray. Males have a bold white line over the eye.
As a spread-winged skipper, this species most often rests with all four of the wings held out flat to the side.
Similar species: The ventral (lower) side is the easiest way to separate this species from Juvenal’s duskywing (Erynnis juvenalis): Juvenal’s has two pale spots toward the tip of the ventral hindwing. Also, by late May, the Juvenal’s duskywing has disappeared; after that, Horace’s is the only duskywing in Missouri with a white spot in the forewing cell.
Larvae are bluish-green with tiny, light-colored spots; head is brown with orange blotches around the margin; body tapers at the end.