For years the territory adjacent to the rivers on the floors of the Sacramento and northern San Joaquin valleys in California has been deluged each spring with hordes of fiercely biting “black gnats.” Certain areas locally known as “black alkali” locations seemed to form the foci from which these pests were blown by winds over wide areas, constituting such a pest in some seasons that agricultural field work was brought to a standstill and even town dwellers were driven indoors until nightfall. The bites are extremely irritating, causing nodular, inflamed swellings that itch persistently for several days or even weeks. In some individuals, particularly those inclined to be stout, the swellings caused by the bite become vesicular, rupture, and produce a moist open lesion that “weeps” a serous exudate for weeks, finally healing with a definite red scar. The insects insinuate themselves beneath the clothing and apparently prefer to bite at some point where their progress is impeded, such as around the hat band, at the belt line, or where the sleeves are closely rolled against the arms, and at the shoe tops. The usual repellents that are effective against mosquitos are of little use against these insects, the only casualties noted being the ones that were actually trapped or drowned in the oily applications used.