Lagria hirta can reach a length of 7–8 millimetres (0.28–0.31 in). These beetles have a soft and elongated body and a head and thorax brown or shiny black. The relatively elongated elytra are yellowish-brown and covered by dense fine light yellowish-brown hairs. The rest of the body is also hairy, but they are less clearly visible. L. hirta's antennae, underside of body and legs are black. This species has eyes, large and round. Antennae are
composed of eleven segments.
The elytra of the females are more extended backward than in the males and the female's abdomen looks from above wider than in the males. The male, in addition to its slimmer body, is distinguished from the females by their larger eyes and by the length of the last segment of the antennae, which is nearly twice the corresponding segment in the female. The hind wings are transparent.