In June, 1909, members of the engineering staff of the University of Michigan were driven from their camp on Douglas Lake in Cheboygan county by the black flies and at the end of the month it was deemed best to postpone for one week the opening of the Engineering Camp and the Biological Station on Douglas Lake on account of these pests. The conditions seemed to demand an immediate investigation and this was undertaken by the writer at the suggestion of Professor Reighard and under his direction.