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.
This fly attacks the host from June to September, depositing its viviparous larvae in the nostrils. The Reindeer attempts to fend off the fly, striking at it with its hoofs and keeping its nostrils closed as far as possible. Once deposited, the lively larvae crawl into the inner nasal passages and as far as the larynx, where they fasten themselves and live on the mucus. A Reindeer may harbor as many as 130 of these parasites. They range from 6 to 26 mm. in length. Their particular growth begins at the end of March, and they are ready for pupation up to May. The host assists their exit by continual sneezing and snuffling. In the last stages they are a great affliction for the host, and they sometimes cause its death. Pupation takes place in or on the ground, under some sort of cover, and it lasts for 15-19 days. The flies have been found emerging from July 12 to 31.
The corresponding parasite of the Barren Ground Caribou is a similar or perhaps identical species, with a parallel life history. Its chief activity as an adult doubtless occurs in July and August. A number of the mature larvae were found in the throat of the buck of June 3; two of them that were preserved measure approximately 7 mm. in diameter and 27 and 30 mm. in length. A large mass of such sizable parasites in the throat might easily become a serious obstacle to comfortable living or even to survival on the part of the host. Presumably the larvae drop to the ground at about the same period as those of _Oedemagena_. Fred Schweder, Jr., remarked concerning the buck of August 17 that these larvae are never found at that season, and Charles Schweder made the same remark concerning a doe specimen of September 21. It would appear either that they remain so small as to escape detection at this time or that they do not reach the throat on their short journey from the nostrils until some later period of the year. Johansen (1921: 24) records larvae only 2-3 mm. long in the nasal passage at the end of May.