Also known as the European mistletoe, iscum album is a parasite found on more than 200 different trees and shrubs. The host plant supplies both water and other nutrients.
Haemoproteus turtur is a blood parasite of turtle doves.
Sparassis crispa is a parasitic fungus, attacks the roots of popular evergreens used as Christmas trees - pines, firs, and spruces.
You know the part in "We Wish You a Merry Christmas" imploring the host to bring out figgy pudding? Apparently, the Philotrypesis caricae attempt to take advantage, establishing parastitic relationships with the fig without providing the benefits of pollination.
Nuytsia floribunda is a parasitic plant that begins to flower around this time of the year - it's popularly known as the "Australian Christmas Tree."
Hypoderma tarandi affects reindeer populations, laying eggs on the animals' skin. After the egg hatches, the parasite burrows into the skin and feeds on host tissue.
Elaphostrongylus rangiferi is another worm that plagues reindeer. The potential danger posed by the parasite is great as it may cause pneumonia-like conditions or, in some cases, confusion and a lack of coordination.
A clue to Rudolph's red nose? The Cepheneymia trompe, also known as the reindeer nose bot fly, like to lay their eggs in the muzzle and nostrils of the reindeer.
Trypanosoma lewisi had a part to play in the elimination of two species of rats native to Christmas Island. Parasites carried by rats that arrived with the ship Royal Mary in 1643 led to the disappearance of a native rat population that settlers initially said were quite large.
Plasmodium vivax is a mosquito-borne disease that some say have played a role in the story behind the magi and the delivery of frankincense.
Macrophomina phaseolina is a fungus found in soil that can rot the tree that produces frankincense.
Hyalomma dromedarii is a tick that tends to be found on camels. No doubt, it was working its mischief back in Biblical times as well.