Discovering the Evergreen Bagworm

When you're a newlywed, there are a lot of "firsts" in your relationship, each one more interesting than the last. One experience I didn't count on having was a run-in with a parasitic caterpillar during our first Christmas.

As soon as we were able, my husband and I went to the Christmas tree farm to cut down a tree. As expected, there was a fair amount of sentiment involved in getting our "first" Christmas tree. We found our tree, cut it down, brought it home and excitedly decorated it. If there were any real flaws with the tree, we couldn't see it. To us, it was the perfect Christmas tree.

I remember noticing a few pine cones hanging delicately off of some of the branches and smiling, undoubtedly thinking something sappy like "Oh it's nature's Christmas ornament!" or something of that nature. Because of that sentiment, I didn't take them off the tree.

Soon after Christmas was over, I was talking to my husband on the phone when I noticed something dripping from one of the pinecones. I took a closer look, thinking it was sap. Then I noticed the strands of silk flowing down to the floor and then the little worms dangling from them. I almost dropped the phone in surprise. Investigation revealed that the cute little "pinecones" were actually bagworm cocoons and the warmth of our home had sped up the hatching process.

The bagworm, often called the evergreen bagworm, is a force to be reckoned with as far as conifers and deciduous trees go. Some of the trees it prefers to feed on are: pine, spruce, cypress, juniper, willow, black locust, sycamore, apple, maple, elm, poplar, oak, and birch.

A bagworm's life begins inside the pinecone-esque cocoon I described. The bagworm's bag is shaped like a spindle and can be 1-½ to 2- ½ inches long and can hold between 300-1000 eggs per bag. When the eggs hatch in late May or early June, the tiny larvae crawl from the bottom of the bag and float down on a strand of silk. Often, this is how the larvae move from place to place, as the wind can pick up the silk and transport the larva along with it. Once the larva lands, it begins to create a new cocoon around itself.

Over time, the larva feeds and grows inside the bag, incorporating bits of its host tree into the cocoon, giving it its textured appearance. Once the larva is mature by mid-August, they may move to a sturdier branch where they attach their bag and settle down to pupate. But while the male hatches within four weeks in its moth form, the females remain inside their cocoon waiting for a mate. After mating, the female mummifies inside the bag around the egg mass, which will lie in wait until spring, beginning the cycle all over again.

The adult males are almost bee-like in their appearance, with a thick furry covering and clear wings. You may be able to spot a larva moving when it sticks its head and front legs out of the top of the bag to feed or move.

You should regularly check your deciduous and conifer trees to make sure they aren't infested. Bagworms are not easily killed when they're hiding inside their thick cocoon. You can spot an infestation by combing the trees for cocoons and by paying attention to their leaves. The bagworms often consume whole leaves, leaving only the veins behind. Young larvae feed on the surface of the leaves, leaving behind small brown spots. They also eat the buds on conifers, which cause excessive dead areas.

So if you're someone who likes to pick out a real Christmas tree, pay attention to those "pinecones." You might be carrying some little friends inside your house!

D.J. Shetlar, Bagworm and Its Control, Ohio State University