Flies of various kinds perhaps cause more wide-spread, year-round misery to the Caribou than all other pests and enemies combined. It is safe to say that not a single individual in the whole population escapes their attacks, and some even succumb to mosquitoes (Gavin, 1945: 228). The various biting and parasitic flies have already been discussed to some extent in the section on Influence of insects on distribution. Harassment by these pests is believed to be the leading cause of the haste with which the Caribou are frequently seen passing over the Barrens in summer. Downes (1943: 204) has commented on the habit of Chipewyan hunters in the Nueltin Lake region of examining the legs of Caribou for swellings caused by mosquito bites. In a buck secured on August 17 the legs exhibited numerous little bumps of this sort; furthermore, black flies covered the buck’s body, while scarcely troubling those of us who were preparing the specimen. Fortunately the suffering from mosquitoes and black flies on the Barrens is largely limited to the months of July and August.
Even at this season the Caribou are granted occasional relief from the blood-sucking flies. The characteristic strong winds of that region help greatly in keeping the insects in abeyance. Furthermore, both mosquitoes and black flies become more or less inactive whenever the temperature drops to the neighborhood of 45° (cf. Weber, 1950: 196), and this happens fairly frequently even in mid-summer. Finally, the black flies retire during the hours of darkness; and short as these hours are, the relief they bring is very noteworthy. These conditions offer something of a contrast to those surrounding the Woodland Caribou. It is difficult to see how that animal can secure a moment’s respite from mosquito attacks, by day or night, through most of the summer. In its forested habitat there is not sufficient lowering of the temperature nor sufficient penetration of strong winds. Hard as the life of the Barren Ground Caribou may be, it seems to have a few advantages not available to the Woodland Caribou; and possibly it is these that have enabled it to attain a vastly greater population than the other species.
Of 52 mosquito specimens brought back from the Windy River area, 39 were Aedes nearcticus Dyar, 2 were probably Aedes fitchii (F. and Y.), and the remaining 11 were of the same genus but not in condition for specific determination (cf. Dyar, 1919; Weber, 1950: 196). Ae. nearcticus is holarctic in distribution; in North America it occurs chiefly on the Barren Grounds, but is known from as far south as Montana. Ae. fitchii ranges through the northern United States and Canada, north to the limit of trees. Of 26 black flies, all were Simulium venustum Say, which occurs in northern Europe, Alaska, and Labrador, south to the Adirondacks, Illinois, Iowa, Georgia, and Alabama. (Names and ranges supplied by Dr. Alan Stone, of the United States Bureau of Entomology and Plant Quarantine.) These mosquitoes and black flies were presumably the species attacking the Caribou in the Nueltin Lake region.
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.
My own observations on the larvae were restricted to a few Caribou specimens in June and in the autumn. As with the Reindeer, the Caribou fawns in their first autumn showed no visible infestation, as I noted in looking over some fresh hides on September 10, and as was noted again in a fawn of September 26. Fred Schweder, Jr., made the remark that larvae would be evident in the fawns by the following spring; this may indicate that the larvae have not, in the autumn, completed their journey to their final position on the Caribou’s back. I learned of no immunity on the part of old adults.
Fullgrown larvae still remained in bucks secured on June 3 (fig. 17) and 18. According to Charles Schweder, they drop out in June. In the buck of June 3 there were perhaps several dozen warbles, each surrounded by a mass of repulsive tissue; in another buck of June 18, there were apparently more than 75. “It may be assumed,” says Johansen (1921: 24), “that the pupae lie on the ground for about a month before the flies appear.” He found (1921: 29) the adult flies abroad at Dolphin and Union Strait by July 14.
In a buck of August 17 the new warbles (or perhaps merely warble scars from the previous June—cf. Banfield, 1951a: 32) on the inside of the skin were not very numerous. Some were medium-sized, but most were so small that it was not deemed necessary to scrape them off; they had comparatively little fatty tissue about them and were merely allowed to dry up. The number of warbles (or warble scars) found in autumn specimens varied considerably, up to a maximum of roughly 200. They were situated mostly along the mid-dorsum, and more on the lower back or rump than farther forward. The number appeared to be approximately 130 in the skin of an adult doe that was nailed to the log wall of a cabin for drying on September 15 (fig. 18). A doe of September 21 seemed to have less than the usual number of warbles.
The nostril fly (Cephenemyia) is another serious dipterous parasite of the Caribou. The life history of the European C. nasalis (L.) (or C. trompe [L.]) and its effect on Reindeer are discussed by Bergman (1917), Natvig (1918), and Jacobi (1931: 245) as follows.