Bot flies are not generally considered festive. This is especially true if you are a reindeer, which often have reindeer nasal bot flies, or snot bots, as they are affectionately known. The nasal bot fly life cycle is a marvelous example of evolutionary WTF-ery.

Adult reindeer bot flies look like harmless fluffy bees, and have a slight buzz to their flight. This fools an unsuspecting reindeer into allowing a female fly to approach its face. The fly doesn't lay eggs on the reindeer. Oh no, it is far more sinister than that. Reindeer snot bot eggs hatch within the mother's uterus. Then she hovers in the air, squirting tiny maggots into the host's nose, using what I can only describe as a weaponized maggot-shooting vaginal gun. The larvae shoot forth in batches of 20 to 30, bathed in "unique uterine fluids."

J. R. Anderson, 2013

The mechanics of this are impressive. A valve between the uterus and vagina clamps shut, and blood and muscles rapidly increase hydrostatic pressure within the vaginal canal. This spurts out tiny maggots in a high speed ejaculation into a reindeer's nose.

The maggots develop for a bit in the deer's nasal passages before burrowing deeper into the sinuses and throat. The maggots' mouths are buried deep in the deer's tissue, which makes you wonder how they breathe? Through openings on their maggoty butt called anal spiracles, of course.

When fully grown, the larvae crawl back to the nasal passages, where a good sneeze or cough expels them into the world. Then the maggots burrow into the ground to spend the winter resting and becoming flies.

By the time the flies emerge in the spring, the herd has moved on. They might find themselves a fair distance from summer grazing areas and unsuspecting deer to infect. That's a problem, these flies must find a hookup and a reindeer nose to reproduce.

No worries: Adult snot bot fly antennae react to the smell of reindeer urine and reindeer interdigital pheromones. When I say "interdigital pheromone" you should read "smelly reindeer toe jam" because that's essentially what it is. The flies can track reindeer for more 30 miles following the scent of pee and toe jam.

Ho Ho ... Holy Hell

Reindeer, moose, or elk bot flies occasionally target unlucky Scandinavian hikers or folks tending reindeer herds. These generally are not nasal bot flies, but if you happen to be the one getting maggots ejected onto your face at high speed, that's probably not at all reassuring. The many case studies will put you off your holiday eggnog. Here's a recent one from Sweden:

"The fly was hovering close to the woman’s face and suddenly ejected larvae into one of her eyes... About 30 whitish larvae were later removed from the eye."

That was describing the first batch of larvae. They had to go back for a few more maggots in a second extraction the next day.

There are species-specific snot bots for camels, antelope, wildebeest, sheep, horses, moose, elks, and kangaroos. It isn't just Rudolph that has a very red nose.

Anderson, J.R. Anatomical modifications, viviparous reproduction and hydraulic expulsion of larvae by Cephenemyia nasopharyngeal bot flies of deer. Medical and Veterinary Entomology (2013) 27, 367–376. doi: 10.1111/j.1365-2915.2012.01060.x

Kan, Boris et al. 2013. Reindeer Warble Fly–associated Human Myiasis, Scandinavia. Emerging Infectious Diseases 19(5): 830–832. doi: 10.3201/eid1905.130145

Kan, Boris et al. 2012. Dermal Swellings and Ocular Injury after Exposure to Reindeer. New England Journal of Medicine 367:2456-2457 doi: 10.1056/NEJMc1201434

Jaenson, Thomas GT. 2011. Larver av nässtyngfluga i ögat - ovanligt men allvarligt problem. Fall av human oftalmomyiasis från Dalarna och sydöstra Finland redovisas. nr 16 sid 928-30.

Bjørn Å. Tømmerås et al. 1993. The olfactory response of the reindeer nose bot fly,Cephenemyia trompe (Oestridae), to components from interdigital pheromone gland and urine from the host reindeer, Rangifer tarandus. Chemoecology 4(2) pp 115-119.