Mistletoe--The Praises of a Parasite

In some cases, it's easy to see how an animal or plant became associated with the holidays. Reindeer pull Santa's sleigh, conifer trees get made into wreaths and used as Christmas trees, and so on and so forth. But mistletoe? It's a rather unassuming plant, one that grows on other plants and gets nutrients from them--a parasite, in other words. And parasites, as we've seen before, usually don't have the best press. But mistletoes is more than just a parasite, and more than just a Christmas decoration. It is, in fact, a keystone plant in many forest ecosystems.

Although mistletoe fruit is inedible to humans, it is eaten by a vast array of other animals, and actually forms a large part of the winter diet of many fruit-eating birds, such as waxwings. Incidentally, mistletoe also indirectly contributes to the spread of other fruit-bearing plants: juniper trees reproduce more successfully if they have mistletoes, because this attracts fruit-eaters that may eat their berries. In Australia, out of the 240 species of birds that nest in the branches of trees, 75% have been recorded nesting in mistletoe.
In southeast Asia and Australia, mistletoe fruit are eaten by small birds called flowerpeckers. These birds, which have specially evolved digestive systems for dealing with mistletoe fruit, are the primary means by which mistletoe plants have spread through the Asian and Australian rain forests. 

The lesson to be learned from this is that there is no single description of an organism's ecological relationships. A mistletoes plant may be a parasite, but at the same time it is also a part of many other interactions in its environment, all of which would fall apart if it were removed. This is why, as environmentalists, we should take into account all living things, even parasites, in our ecological plans.

A cluster of mistletoe grows on a tree, green against the white and brown of winter. Although it is a parasite, mistletoe has a surprisingly important role in many ecosystems.