Tenthredo monilita can reach a length of about. These sawflies are quite variable. They usually have a black head, with yellow mouth parts. The antennae are entirely black. On the front of the thorax there is a small yellow stripe. On each side of the 1st tergite there is a white spot. The 3rd, 4th and 5thsegments of the abdomen are reddish, while the apical segments are black. The legs are mostly brown, with black femurs. Wings are mostly transparent, with brown veins. In males the abdomen is more reddish.