Every day spent hiking out in our forest brings more mysteries to be answered. This week let’s explore some partially “parasitic” partnerships that have always fascinated me out on trail.


Insect gall

Ever see a round woody ball growing out of a tree branch? Often it’ll have a random pattern of little holes dotting its smooth surface. You are looking at a bona-fide insect larvae condo.

An insect gall is a custom construction project of living plant tissue with the resident insect playing lead contractor. In order to hijack plant growth to form galls, the insect must seize a time when plant cell division occurs quickly. In our part of the world, that means spring.

The insect (and/or its larvae) feeds on the rapidly growing plant tissue while injecting chemicals to encourage further growth. Quickly growing (meristematic) tissues like buds, bark and leaves are most vulnerable to these little guys.

After the gall is formed, the insect larvae develop inside until fully grown. Galls provide the industrious little larvae with not only a four-course buffet, but their own impenetrable fortress, protecting them from predators as they grow. When they are ready, they bore out an exit hole and venture out into the wide world.

Although insect galls get bad raps for their role as “unsightly” tumors on plants, they are completely harmless. The insects are usually excellent caretakers and make sure their construction projects do not threaten their hosts.

Most species even provide an overall benefit for their host or local environment, including quite helpful pollination services for plants, and food sources for our beautiful birds and bats.



Particularly noticeable in winter as an oddly green bushy clump high up in the barren branches of trees, mistletoe is a (in)famous parasite that attaches itself to trees and shrubs, pirating water and nutrients from its host.

American mistletoe’s scientific name, Phoradendron, means “tree thief” in Greek. However, mistletoe’s common definition as a tree-killing pest may be too simplistic a view. Mistletoe may take from the tree for its own survival, but it pays back to the local ecology in several unexpected ways.

Despite its nasty reputation, studies reveal that an abundance of mistletoe in a forest means many more kinds and numbers of birds and critters can thrive there. An amazing variety of critters rely on mistletoe for their food, especially in winter.

Animals from birds to squirrels, chipmunks, porcupines and even deer eat the leaves, tender young shoots and juicy berries, leaving behind mistletoe seeds in their droppings. These seeds will again grow into mistletoe’s Medusa-like masses of branching stems, providing excellent shelter and nesting sites for many animals.

The northern spotted owl is always on the lookout for a nice mistletoe to settle down in. The caterpillar stage of several beautiful butterfly species also use mistletoe greenery as their shelter and as their only food.

Even better, mistletoe flowers often provide the very first pollen available in the spring for extremely hungry honeybees and native bees. Thus, although it can shorten the life of some trees, mistletoe can also have a very positive effect on our forest, providing high-quality nutrition and homes for a broad range of critters.

So next time you get a chance, take another look at these “bad guys”.