On February 13, 1954 a heavy infestation of small galls was noted on a growth of willow shrubs (Salix sp.) in London Township about a mile north of London, Ontario. The exact location was on the north bank of the North Branch of the Thames River about 100 yards west of the bridge by which Adelaide Street crosses the river. The bushes were crowded along the bank and several of them had their lower branches under water and their roots extending well out into the mud of the river. The galls were one-eighth to three-eighths of an inch long (Fig. 1) and were roughly spherical to oval in shape. The bark of a gall was scarred by shallow furrows running along its length. At its upper end each gall bore the scales of a withered bud or an oval scar from which the scales had fallen. Flanking the scar were two rounded swellings of incipient buds. Many of the galls were separatelv developed along the twigs, being well apart from one another, hut in some cases they were crowded against one another so that three or four galls occupied one inch of the length of the twig, and in several instances a number of adjacent galls had coalesced to form an irregular swelling one or two inches long, along the length of a twig. In the key to insect galls of willow in Felt (1940) the galls were identified as scarred willow galls caused by the gall fly Phytophaga tumidosae (Felt).