If your household celebrates Christmas, and if you prefer to use a natural tree to do so, you may end up bringing in more than just a beautiful evergreen. Firs, pines, and spruces can all harbor a multitude of arthropods nestled in their foliage or even living under the bark. In the field, Christmas tree growers combat a variety of insects that could damage the tree before harvest, but the ones you might deal with in the home are called “post-harvest” pests, and they are similar to fall invading insects when they pop up in the house.
Christmas Tree Invaders
Some of the critters hiding out in the tree may be adults using the tree as an overwintering site. In the tree outside, they would be protected from the colder air temperatures of winter and hopefully be safe from freezing. Once they come inside though, our interior heating will warm them up and allow them to start moving around. This group can include large and obvious specimens like spiders and stink bugs, as well as smaller, harder to detect types, like barklice and predatory mites. Many of these may stay with the tree, but if they do start to wander, they are unlikely to survive very long in our dry, winter homes.
The other invaders with Yuletide spirit are likely hiding in the tree as eggs or as pupae. These immobile life stages in insect development are common overwintering stages as they are protected and don’t need inputs to survive. Insect development is temperature-dependent, though. When eggs or pupae are outside, the cold temperatures will delay them from hatching until spring when temperatures start to perk up. When they come into our consistently 68- to 70-degree homes, though, they start developing rapidly and will be able to hatch or emerge just in time for Christmas dinner. Hitchhikers in this group can include aphids, scale insects, and spiders. One interesting insect egg case that may come with your tree is made by a praying mantis. Mantids create an ootheca, an egg case that looks like spray foam insulation and protects their eggs. These can be on the trunk or twigs of a tree and hard to spot; some mantids seem to prefer fir trees for their egg laying site.
Bark beetles may be under the bark of the tree as pupae. The adults could emerge from these pupae more quickly thanks to the indoor heating, as well. The larvae of these small beetles (1/4 inch or less long as adults) live and feed in wood. Even though they utilize wood, these beetles will not be interested in infesting the lumber of your home. In fact, none of the aforementioned arthropods pose a hazard to homes, pets, people, or stocking stuffers. You can always easily vacuum them up and dispose of them.
What to Do (and Not Do)
There is an association between these post-harvest pests and warmer autumn temperatures. These pests aren’t necessarily something that the Christmas tree grower/seller could have prevented. When you buy your tree, you might see it get shaken by a machine to try and dislodge any unwelcome guests. But usually the harvest, transport, and purchasing of the tree is enough to discourage arthropods from hanging out. Those hitchhikers that make it through this process result in a relatively rare phenomenon, but one that can still be startling if it happens to you!
Again though, these accidental houseguests shouldn’t cause much concern. Vacuuming, spritzing individuals with soapy water, or sweeping them outside are all acceptable responses. Bug bombs, liquid sprays, or other insecticides should not be used on the tree. These residues could be hazardous to people and are not likely to provide good control in this situation.
By Jonathan Larson; Entomology Extension Specialist