Deer Nose Bots
Description and Distribution
Aristotle almost certainly described larvae of Cephenemyia, commonly known as deer nose bots, when he wrote, "Without any exception stags are found to have maggots living inside the head, and the habitat of these creatures is the hollow underneath the root of the tongue, and in the neighborhood of the vertebrae to which the head is attached. These creatures are as large as the largest grubs; they grow altogether in a cluster, and they are usually 20 in number".
Deer nose botflies have been reported from nearly all areas of the continental U.S. and Canada. They have not been reported from the Great Plains, Ohio, Kentucky, Tennessee or Alabama. An unidentified species has been reported from white-tailed deer in Florida. Interestingly, the known distribution of the parasites does not completely cover the geographic range of potential cervid hosts.
There are at least five species of Cephenemyia in North America: C. apicata in the west, infecting mule deer; C. jellisoni in the northwest, infecting mule deer, white-tailed deer, moose and elk; C. phobifer in the northeast, infecting white-tailed deer and moose; C. pratti in the southwest infecting mule deer and white-tailed deer; and C. trompe in the north, infecting white-tailed deer and caribou.
C. phobifer is the only species known to occur in Michigan. A survey in the 1970's showed the parasite was quite common in adult deer in both Regions I and II in the spring, and rare in those from Region III. Deer less than 1 year old are not quite as apt to have nose botfly larvae as are adults.
Transmission and Development
The eggs of Cephenemyia hatch in the uterus of the female fly and while in flight she ejects minute larvae into the nostrils of the host deer. The larvae migrate to the retropharyngeal pouches which lie on either side of the throat at the base of the tongue. There they become attached in clusters and develop.
Developing larvae are white; while fully developed larvae are about 25 to 36 mm long and yellowish-brown. When the larvae have completed their development, they are expelled from the throat. They then seek a suitable place in the soil to pupate and after a relatively short pupal period (2 to 3 weeks) adult flies emerge. The adult flies have no mouth parts for feeding so they are short-lived and must mate shortly after emerging, thus completing their life cycle.
There may be two generations a year of C. phobifer in Ontario and Michigan white-tailed deer. In these areas, the winter cycle requires about 6 months of development and the summer cycle about 3 months.
Clinical Signs and Pathology
External signs of the presence of deer nose bots are seldom noticeable. Behavior such as snorting and lowering of the head may indicate the migration of released mature larvae within the nasal passages. Nasal discharge and giddiness may also become evident. Occasionally, heavy infections may cause death by suffocation. Death may also result from detached larvae migrating to the lungs.
The retropharyngeal pouch is usually enlarged in infected deer and may become markedly inflamed. The epithelium of the pouch appears pitted or eroded and may become partly detached, necrotic and edematous.
Diagnosis of nasopharyngeal myiasis (nose bots) consists merely of finding the larvae within the host. In order to identify the larvae to species, it is usually necessary to rear them to the adult stage.
Treatment and Control
Treatment and control of nose bots in wild deer is impractical and apparently unwarranted. In penned deer, the application of pine tar to the muzzle has been recommended.
Cephenemyia species are known to infect only deer, and meat from these animals is suitable for human consumption, thus there is no public health significance. They are apparently well tolerated by white-tailed deer and cause no problems. However, C. trompe is considered to be a serious problem in domestic reindeer management in Scandinavia. It is estimated that in Sweden, the losses due to C. trompe and the grub fly (Oldemagena tarandi) amount to about 2 million Swedish crowns per year, which is approximately 15% of the income from reindeer production.
For questions about wildlife diseases, please contact the Michigan DNR Wildlife Disease Laboratory.