[1] An elongate, woody swelling (up to 10 mm long) of the mid-rib of a leaf which can extend into the base of lateral veins and the petiole.

The gall is more prominent on the underside of the leaf and is initially green, later red-purple and brown.

Each gall contains a single larve which are white or yellowish when young and red when mature, with a weak sternal spatula.

[2] Mature larva leave the gall in late summer to hibernate and pupate in the soil.

[4] Massalongia rubra has been recorded from Belgium, Czech Republic, Germany, Great Britain, the Netherlands and Sweden.