[1] Tenthredo olivacea can reach a length of about 8–14 millimetres (0.31–0.55 in).

Head, thorax and abdomen have black markings.

The dorsal surface of femur, tibia and tarsus shows a black line.

Though similar to Rhogogaster viridis, it has a thinner body.

Moreover R. viridis shows black rings on tarsi.