Not Just for Kissing: Mistletoe and Birds, Bees, and Other Beasts

Perhaps some of you have already experienced a sweet holiday smooch or two under the Christmas mistletoe, enjoying this fairly old kissing ritual for people. But mistletoe is important in other vital ways: it provides essential food, cover, and nesting sites for an amazing number of critters in the United States and elsewhere. In fact, says Rob Bennetts, a USGS research scientist, some animals couldn’t even survive without mistletoe, including some birds, butterflies, and insects. But first, a little bit about the plant. The white-berried Christmas mistletoe we hang so hopefully in places where our sweethearts will find us lingering, is just one of more than 1,300 species of mistletoe worldwide. Globally, more than 20 mistletoe species are endangered. Two kinds of mistletoes are native to the United States: the American mistletoe (the one commonly associated with our kissing customs) and the dwarf mistletoe. American mistletoe is found from New Jersey to Florida and west through Texas. The dwarf mistletoe, much smaller than its kissing cousin, is found from central Canada and southeastern Alaska to Honduras and Hispaniola, but most species are found in western United States and Mexico. Mistletoe is no newcomer to this country: excavations of packrat middens reveal that dwarf mistletoes have been part of our forests for more than 20,000 years. Some fossil pollen grains even indicate that the plant has been here for millions of years. Says Bennetts: “Mistletoes should be viewed as a natural component of healthy forest ecosystems, of which they have been a part for thousands, if not millions of years.”

Thief of the Tree

The thing that all mistletoes have in common is this: all grow as parasites on the branches of trees and shrubs. In fact, the American mistletoe’s scientific name, Phoradendron, means “thief of the tree” in Greek. The plant is aptly named: it begins its life as a handily sticky seed that often hitchhikes to a new host tree on a bird beak or feather or on mammal fur. In addition to hitchhiking, the dwarf mistletoe also has another dandy way of traveling to a new host tree: the seeds of this mistletoe will, like tiny holiday poppers, explode from ripe berries, shooting a distance as far as 50 feet. One researcher said that if you put ripe berries in a paper bag and shake it, it sounds just like popping popcorn. For the most part, the mistletoe is pretty darn cavalier about what host tree it finds — dwarf mistletoes like most kinds of conifers; American mistletoes are found on an incredible variety of trees. Once on a host tree, the mistletoe sends out roots that penetrate the tree and eventually starts pirating some of the host tree’s nutrients and minerals. In actuality, though, mistletoes are not true parasites; instead they are what scientists call “hemi-parasites” because most of them have the green leaves necessary for photosynthesis. Still, it seems like a pretty lazy life for most mistletoes: a little photosynthesis here and there and a lot of food and water stolen from their unsuspecting benefactor trees. Eventually, mistletoes grow into thick masses of branching, misshapen stems, giving rise to a popular name of witches’ brooms, or the apt Navajo name of “basket on high.”