The adults of Arge cyanocrocea grow up to 7–8 millimetres (0.28–0.31 in) long.[4] As all sawflies, this species is related to wasps and not to flies, but lacks the typical wasp waist. Its head and thorax are black, while the abdomen is yellowish orange. Legs are reddish, with small black rings. The wings show a characteristic wide transverse dark band and gray apex.[5][6]Arge cyanocrocea is rather similar to Arge pagana, that shows black wings.[5]
The larvae of this species look like caterpillars, but they have five pairs of prolegs, while caterpillars have four pairs. They feed on the leaves of brambles (hence the common name), mainly blackberry (Rubus fruticosus), raspberry (Rubus idaeus) and great burnet (Sanguisorba officinalis).[3][4]
