If you celebrate Christmas, mistletoe may seem like an essential part of the season. For many animals, however, mistletoe plants truly are a necessary part of survival during at least one season of the year.
There are 1300 species of mistletoe. All are parasitic plants that live on the branches of other trees, send roots into those branches and help themselves to the trees’ nutrients and minerals. The name of one mistletoe genus, Phoradendron, even means tree thief. Mistletoe has a negative effect on tree lifespan, so forests with high rates of mistletoe have more dead trees, which provide homes for cavity-nesting birds. As a result, more cavity-nesting birds live in forests with vibrant mistletoe populations.
Several butterflies depend on mistletoe. The great purple hairstreak feeds on American mistletoe (Phoradendron serotinum), the species which has long been associated with the tradition of kissing in humans. This butterfly lays its eggs on the mistletoe and the caterpillars feed on it after hatching. Two other butterfly species feed on dwarf mistletoe: Johnson’s hairstreak and thicket hairstreak butterflies court and mate on mistletoe and then lay eggs there. Johnson’s hairstreak caterpillars are green and mottled, providing them excellent camouflage as they feed on the mistletoe. Adults of all three of these species feed on nectar from mistletoe flowers.
Native bees eat both pollen and nectar from mistletoe. Mistletoe pollen is typically the first kind available to bees in the spring, making it an important food source for them. Bees are the most important pollinators for this plant, although many other insects such as flies, ants and beetles also feed on the pollen and perform some pollination. There are also thrips and mites whose associations with dwarf mistletoe are quite strong.
Many birds eat mistletoe berries, including Bluebirds and Robins. Phainopeplas, a type of silky flycatcher that lives in Arizona, is especially dependent on mistletoe, relying almost exclusively on this plant for food in the winter, and eating over 1100 mistletoe berries each day when they are available. If the mistletoe produces a light crop of berries during spring, Phainopeplas may not breed that year. The plant and the bird both benefit from this relationship, as Phainopeplas are the species most likely to disperse seeds to suitable spots for a new plant to grow. Mistletoe seeds are very sticky, even after passing through the gut of a bird. When birds leave their droppings on branches, the sticky mistletoe seeds adhere to the spot, giving a new plant the opportunity to grow in a favorable location. The name mistletoe is Anglo-Saxon in origin, and means dung-on-a-twig.
Quite a few birds nest in mistletoe, including Spotted Owls, Cooper’s Hawks, Chickadees, Mourning Doves, House Wrens and Pygmy Nuthatches. Squirrels also commonly use these plants as nesting sites in addition to feeding on them. Other mammals also eat mistletoe with species as diverse as elk, porcupines, deer and chipmunks regularly making use of this resource.
Mistletoe is good to so many species. May it be good to you this season, too.
Karen B. London, Ph.D. is a Certified Applied Animal Behaviorist, Certified Professional Dog Trainer, author, and an Adjunct Faculty in NAU’s Department of Biological Sciences.
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