I tend to think of Rudolf the red-nosed reindeer as being part of the rather tacky side of Christmas which has never greatly appealed to me, but the other day I came across a reference in a free magazine that came through my door which I thought was worth investigating. A section on 'festive oddities' claimed that 'Rudolf's red nose is based on fact', and that the membranes of reindeers' noses do indeed become inflamed and red as a result of parasitic infections provoked by rummaging for lichens under the snow.
Searching of CAB Abstracts revealed that the main parasite to be found in the noses of reindeer is the nasal bot fly, Cephenemyia trompe, which is quite common (average prevalence in a series of studies1 in Norway was 65.2%). Once I knew the species it was easy to find further information in CAB Abstracts, the CAB Abstracts Archive and the CABI book The oestrid flies (information below without footnotes is from the book).
The adult flies (which are round and furry like bumble bees, as a protection against potential predators) are active in summer, and can fly many miles to keep up with the deer. The females give birth to larvae rather than laying eggs, and they spray them at the deer's muzzle from several centimetres away; the larvae then migrate into the nasopharyngeal region via the nostrils or the mouth. The first stage larvae may become dormant in the nasal cavities over the winter, before developing to the second and third stages in the pharyngeal pouches in the spring. They leave the host (inducing severe sneezing) prior to pupation.
Although moderate infestations with flies of the family Oestridae are often well tolerated by the hosts, parasitic and blood-sucking insects do have a significant effect on reindeer behaviour2, disturbing their foraging and increasing energy expenditure. The presence of C. trompe in particular causes them to become agitated and hide their noses in the vegetation3 to try to avoid oviposition. The larvae cause significant inflammation inside the nasal cavities, and severely infested animals sometimes die; but I couldn't find anything to indicate that the outside of the nose ever looks red!
Older reindeer are less affected than younger ones4, similar to the pattern noticed with the related species Oestrus ovis in sheep, probably because of acquired immunity. As for what Father Christmas should do if his reindeer are infested, a range of insecticides from the avermectin group are effective against C. trompe5,6, and darkened shelters for the deer to hide in can help protect them from the flies7.
From this we can conclude that intriguing pieces of information in free magazines should neither be taken at face value nor ignored altogether; it can be interesting to find out the facts that may be behind them.
Happy Christmas and New Year to our readers.