Pamphilius balteatus belongs to a rather small family of Sawflies: the Leaf-rolling Sawflies, also known as the Web-spinning Sawflies (Pamphiliidae). The larvae in this family either roll up a leaf using silken wires to feed inside, or they spin some leaves together to live inside this self made home. The latter method is especially used by species feeding on conifers. They have rather long, simple antennae looking like straight wires. There are only some 200 species in this family, of which some 28 occur in Europe.
Looking from above Pamphilius balteatus can be told apart from other Leaf-rolling Sawflies by the almost completely black head and thorax. There are only two small yellow lines on the head and the shield is yellow as well. But no more yellow markings are visible, making it one of the most unmarked and darkest representatives of its family in Europe. Typically this species will reach a length of some 11 to 14 mm.
The larvae live inside a rolled up leaf, on which they feed. After a while they may move to another leaf, still inside the old one. The larvae are usually found on plants belonging to the Rose-family, but may feed on members of the Birch-family or other catkins bearing trees. Adults are seen in May and June, larvae from June to September.
In Britain this is an uncommon species, usually appearing locally on sandy soils. In most of its area it is a rather local species. But it has a vast area: from Portugal to Kamchatka. Recently even discovered breeding in Japan.