Susan Perkins at the American Museum of Natural History is almost done with a truly heroic feat: overseeing a blog that features a new parasite every day in 2010. As we glide towards the end of the year, she’s launched “The Twelve Parasites of Christmas.” So far, mistletoe (that botanical equivalent of a tapeworm!), two turtle doves (and their blood parasites), and the cauliflower mushroom, bane of Christmas trees. What gifts await us in the next week?