Nasal Bots in Deer
The first time I saw nasal bots happened when I was removing the retropharyngeal lymph nodes from a deer that
had recently died and needed a CWD test. Needless to say, I was not sure what these maggot like worms were
doing in the throat of this deer and if I had just found some new disease of whitetail deer. After a little research, I
found out that these parasites are quite common and have found them many times since.
Nasal bots are the larvae or "maggot stage" of a specialized fly that belongs to the genus Cephenemyia. These
bots are specific to cervids meaning only members of the deer family can have these. Nasal bots begin life when
the adult fly lays a group of eggs around the mouth or nose of deer. The small larvae are released from the eggs
when the deer licks them. The larvae them migrate to the nasal passages where they molt into larger stages of the
maturing larvae. The mature larvae then move to the retropharyngeal pouches which lie on either side of the throat
at the base of the tongue. Here they grow to over an inch in length, are yellowish-brown in color and attach in
clusters deep in the throat. When the larvae have completed their development, they are expelled from the throat.
The deer may snort and lower the head to try to blow out these larvae which then burrow into the soil to pupate and
after a relatively short pupal period {2-3 weeks} adult flies emerge.
External signs of the presence of nasal bots are seldom noticeable. Snorting, nasal discharge, and a nervousness
can occur when the bots are being expelled. The bots are apparently well tolerated by deer and do not cause any
significant disease. Treatment and control of nasal bots is somewhat impractical as the fly can produce at least two
generations a year. Deworming your deer with an ivermectin product will kill the bots but only protect against
reinfection again for about 3-4 weeks.
So what do you do if you find nasal bots? They look like they would make great bluegill bait!!! Take a few fishing
and let me know!
Dr. Mike Strobush
Grassland Vet Service