The effects of the two parasitic flies are felt nearly throughout the year. The adult warble fly (_Oedemagena tarandi_) is seen in the Windy River area in August, when the Caribou are on their southward march. On August 22 Fred Schweder, Jr., secured three of them on freshly killed Caribou and another that alighted on himself--all on an island in Windy Bay. His name for them is “deer fly.” He reported seeing about 50 of them on this day (more than ever before), although he sighted only 10 Caribou. As he remarked, these fuzzy flies look much like bumblebees. Three days later, along Little River, something buzzed past me while a band of Caribou were near. It was probably this species, although it suggested a hummingbird almost as much as a bumblebee. On several subsequent August days, while numbers of Caribou were passing very close to me, I detected no more of the warble flies. In general, they might well have escaped my notice owing to my preoccupation with photography; but on August 30, when I looked for them on one of the nearest animals, I saw none. Evidently they are not sufficiently numerous (like horse-flies on cattle) to be constantly in attendance on each Caribou. In fact, a comparative scarcity (or at least difficulty of capture) may be surmised from the fact that the Canadian Arctic Expedition 1913-18 brought back only three adult females--one from Teller, Alaska, and two from Bernard Harbour, Dolphin and Union Strait (Malloch, 1919: 55). Weber (1950) collected no Oestridae in Arctic Alaska. Apparently there has been scarcely any published study of the egg-laying or other habits of the adult _Oedemagena_ in relation to _Rangifer arcticus arcticus_, other than a few recent notes by Banfield (1951a: 31-32, fig. 17); but its behavior in relation to the Lapland Reindeer seems to be fairly well known, and it is summarized by Jacobi (1931: 245-246). In the case of the Reindeer, the fly’s eggs are laid (during the summer) generally on the legs, belly, and tail region of the victim; the larvae, on hatching, bore through the skin, travel widely through the body, and finally (in the autumn) reach the place for further development--beneath the skin of the back on both sides of the vertebral column. Each one makes a breathing-hole through the skin, and uses this as an exit when leaving the host in the following June. Only the younger animals, from one to about four or five years old, are heavily infested; those still older are spared, possibly having learned to guard themselves better against the fly. Curiously enough, the fawns are said to escape this parasitism entirely.