As a child and young adult, we always cut a live tree for Christmas. It was a family tradition and something our family looked forward to during the holidays. However, along with a live tree also came an assortment of critters that had made their home in the tree during the growing season.
There are a variety of insects that inhabit evergreens, including scales, bagworms and mites. None of these insects pose any threat to humans. No, they just like to use your Christmas tree as their home. Bear in mind that they were living in the tree long before you decided it would look great in your living room.
Usually these insects die out, as indoor temperatures and humidity are not conducive to their development. And in general, they will not leave the tree, as that is their habitat and source of food.
• Scales. Pine needle scale is probably the most common scale insect to inhabit pines and spruces. Scales are found on the needles; they are flat, about an eighth inch long, elongated and white. A heavily infested tree may look like it has been flocked, so if you like that appearance, then you are all set.
The downside? Outside, the scale overwinters as an egg, so if your tree is in a warm environment long enough, some of the scale eggs may hatch, and the young “crawlers” may move around on the needles. They pose no threat to us.
• Bagworms. This past season, a lot of evergreens (i.e., cedars, pines, spruce, arbor vitae) were infested with bagworms. In nature, bagworms are serious defoliators of evergreens and can put plants under stress. If you select an infested tree, you will notice 2-inch-long “bags” attached to the twigs and branches. The bag is made of silk produced by the larvae and will also contain foliage from the host plant.
Bagworms feed on both evergreen and deciduous trees, and the outside of the bag will reflect tree foliage. On evergreens, the outside of the bag will resemble pine needles or leaves of junipers or arborvitae. On deciduous trees such as maples, lindens and honeylocust, the bag will have a “flaky” appearance like partially decomposed leaves. The bagworm overwinters as an egg and will hatch next spring; however, like scales, if they are exposed to warm temperatures long enough, they may hatch and emerge from the bag. Again, they are harmless to humans, and there’s no need to worry.
• Plant mites. Plant mites only feed on plants, not people or pets. They are sap-feeding animals and may overwinter as eggs, immatures or adults. Mites are very small, so you may not even notice them until they start moving around. Spider mites will form a light webbing in the foliage, which is easy to see. If you had a garden this past summer, you may have seen them feeding on tomatoes and peppers.
Remember, the development of insects and mites is regulated by temperature and day length. Like us, they become more active the warmer it is, which means they will think it is spring if you expose them to warm temperatures long enough. None of these critters are “programmed” to live indoors, so you do not need to be concerned about them infesting your house. If they do show up, just share some Christmas cheer, give them some eggnog and enjoy nature.
Have a merry Christmas and a safe and prosperous new year!
Miller is a horticulture professor at Joliet Junior College in Joliet, Ill., and a senior research scientist in entomology at The Morton Arboretum in Lisle, Ill. Email your tree questions to him at firstname.lastname@example.org.