Dr. Fitch describes this fly as follows: "It has a considerable resemblance to the common house fly, though when the two are placed side by side, this is observed as being more slender in its form. The two sexes are readily distinguished from each other by the eyes, which in the males are close together, and so large as to occupy almost the whole surface of the head, while in the females they are widely separated from each other. These flies are of an ash gray color, with the head silvery, and a rusty black stripe between the eyes, forked at its hind end. And this species is particularly distinguished by having a row of black spots along the middle of the abdomen or hind body, which sometimes run into each other, and then forming a continuous stripe. "This row of spots is quite distinct in the male, but in the female is very faint, or is often wholly imperceptible. This fly measured 0.22 to 0.25 inch in length, the females being usually rather larger than the males." The eggs are white, smooth, somewhat oval in outline, and about one twenty-fifth of an inch in length. Usually not more than half a dozen are laid on a single plant, and the young maggot burrows downward within the sheath, leaving a streak of pale green to indicate its path, and making its way into the root, devours all except the outer skin. [Illustration: FIG. 10.] The maggots reach their full growth in about two weeks, when they are about one-third of an inch long, white and glossy, tapering from the posterior end to the head, which is armed with a pair of black, hook-like jaws. The opposite end is cut off obliquely and has eight tooth-like projections around the edge, and a pair of small brown tubercles near the middle. Fig. 11 shows the eggs, larva, and pupa, natural size and enlarged. [Illustration: FIG. 11.] They usually leave the onions and transform to pupæ within the ground. The form of the pupa does not differ very much from the maggot, but the skin has hardened and changed to a chestnut brown color, and they remain in this stage about two weeks in the summer, when the perfect flies emerge. There are successive broods during the season, and the winter is passed in the pupa stage. The following remedies have been suggested: Scattering dry, unleached wood ashes over the plants as soon as they are up, while they are wet with dew, and continuing this as often as once a week through the month of June, is said to prevent the deposit of eggs on the plants. Planting the onions in a new place as remote as possible from where they were grown the previous year has been found useful, as the flies are not supposed to migrate very far. Pulverized gas lime scattered along between the rows has been useful in keeping the flies away. Watering with liquid from pig pens collected in a tank provided for the purpose, was found by Miss Ormerod to be a better preventive than the gas lime.