Macrophya montana can reach a length of 8-12mm. This species shows an evident sexual dimorphism. The females are recognisable by the yellow markings on the abdomen and hind legs. These marking are absent on the abdomen of the males, that are completely black. The legs are mostly yellow with black markings in both sexes. The adults of this sawfly can mostly be encountered from May through July. Adults mainly feed on pollen and nectar. The larvae develop on the leaves of blackberries and raspberries (Rubus species).