Well, the holidays are upon us and that means the weather is getting cold. Sometimes it's hard to talk about insect pests when most of them have hopped a bus and are headed to Arizona for the winter.
Occasionally, however, there are insect problems that occur during the winter. Something that rarely occurs but does happen when the fall weather is warm is that unwanted small creatures enter the home by hitching a ride on your Christmas tree. These small creatures are not elves, but are usually aphids or mites.
For me, picking out a real tree from a local tree farm is an enjoyable family moment, one of our favorite things. One time, however, after we set up our tree, several hundred moving dark spots appeared on our walls. In our case, these were aphids. Every Christmas tree can harbor insects, mites, or spiders. Some of these may remain on the tree into winter and could become active after being exposed to the warm temperatures inside the home. The good news is that this doesn't happen very often, and none of these accidental introductions are a threat to your home, its contents, or occupants.
The Pennsylvania Dept. of Ag has some good tips. Preventing introduction of these guests into your home is the best, and easiest, plan. Mechanical tree shakers, available at some retail lots, are useful in removing some insects from the trees. Vigorously shaking the tree before bringing it into your home will serve the same purpose. It will remove any loose needles, as well. Bird nests, although considered decorative by some people, may contain bird parasites such as mites and lice. They should be removed by hand if not dislodged by shaking.
Control of these temporary invaders should be limited to non-chemical means. Aerosol insect sprays are flammable and should NOT, under any circumstances, be sprayed on the Christmas tree. Any that collect on ceilings, walls, or windows can be eliminated with a vacuum cleaner. Do NOT crush them as they will stain your walls. Remember that these bugs are normally found outdoors, on LIVE trees. If any escape the vacuum, warm temperatures, low humidity, and lack of appropriate food conditions typical of most homes usually will kill these invaders in a short time.
No Christmas tree will have every pest on the following list. In fact, most will be free of these hitchhikers. Occasionally, however, one or more of the following may find its way into your home on your tree.
Occasionally, aphids will hatch from Christmas trees in sufficient numbers to cause alarm. Most aphids are tiny, inactive, and usually go unnoticed. Some Cinara aphids may reach a length of nearly 1/8 inch. Most forms, especially those of early generations, are wingless and remain active throughout their lives. The photo to the left is of conifer aphides, by Wilson, USDA.
With their brownish or blackish coloration and long legs, Cinara aphids may be mistaken for small spiders or ticks. Aphids, however, have only six legs, while spiders and ticks have eight. Also, these insects do not produce silk or webs, typical of spiders.
On true firs, balsam twig aphid may occur. This gray-green species is much smaller than the spider-like Cinara aphids found on pines and spruces. Outdoors, their overwintering eggs normally hatch in very early spring; indoors, they may hatch before the Christmas tree is removed. They are less likely to be abundant than Cinara aphids. All aphids on Christmas trees are host-specific, meaning they can only survive by feeding on certain plants. They will not feed on your houseplants.
Many species of predatory mites overwinter as adults and become active when exposed to warm temperatures in the home. They generally remain on the tree, where they may prey on insect and mite eggs. Most of these tiny, light-colored mites will go unnoticed. One type, however, is bright red and rather large. These predatory mites are relatives of chiggers, but are not a threat to people or animals. Several species of bird parasites may be found in nesting material after the birds have abandoned the nest. Although these mites are generally not present on the trees in winter, bird nests on the tree should be removed to assure that no mites are brought into the home.
Sometimes a tree (especially white pine) will seem to develop its own "flocking" on twigs and bark. This is probably due to the pine bark adelgid, a tiny, aphid-like, sucking insect that secretes cottony wax filaments over its body. These adelgids are sedentary and do not leave the tree, but the spontaneous "flocking" may be a cause for curiosity or even concern. These adelgids, and the "flocking" they produce, shown in the photo to the right by Jim Kalisch of UNL Extension, are harmless.
These insects are sometimes, unfortunately, referred to as "bark lice," a name that is misleading since there is nothing louse-like about them. Psocids are small, winged, soft-bodied insects, colored gray or brown. "Bark lice" are not parasitic and do not bite, but feed on a variety of materials, including fungus, mold, pollen, and dead insects. They can be found outdoors on the bark of many trees, including Christmas trees, but will quickly die from conditions in most homes.
Crawlers of scale species that overwinter in the egg stage may appear on trees kept indoors long enough for eggs to hatch. The most likely candidate is the pine needle scale. If its populations are high, large numbers of red crawlers moving about on the tree may be mistaken for mites, "lice," or some other tiny insect. These crawlers could easily be shaken or knocked from the tree and may be noticeable (especially on a light background) as tiny, slowly moving red specks. If crushed, they may leave red spots or streaks that can be removed with soapy water.
Pine tortoise scale (photo to the left by Jim Kalisch, UNL) and striped pine scale will not produce crawlers indoors. Both scales overwinter as immatures and do not have sufficient time to mature and produce offspring on trees kept indoors. If they begin to feed, however, they may excrete small amounts of a clear, sticky liquid known as honeydew.
Spiders found on Christmas trees are predators of insects and are not dangerous to people or pets. They are either overwintering species that have become active or spiderlings that have hatched after being exposed to warm temperatures. In most cases, they will remain on the tree and go unnoticed. But, if they venture off, they may weave small webs on walls, ceilings, or furniture. These webs, and their inhabitants, can be removed easily with a vacuum cleaner or dusting brush. It is important to remember that the spiders brought in with the tree are not indoor species and will die in a short time because of their new, unsuitable environment.
Enjoy your Christmas tree even more, now that you know what hitch hikers may appear, and what to do about them!