|Source: Rayanne D. Lehman and James F. Stimmel
Pennsylvania Department of Agriculture, Bureau of Plant Industry
Purchasing a REAL Christmas tree may be a big decision for many people, but fears of introducing unwanted and potentially harmful pests into the home via the tree are unwarranted. rSome of these may remain on the tree into winter and could become active after being exposed to the warm temperatures inside the home. Although many will stay on the tree, a few may be attracted to sources of light, including windows. But, because they are associated with field-grown conifers, none of these accidental introductions are a threat to your home, its contents, or occupants.
Preventing introduction of these “pests” 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, and will also remove any loose needles. 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. Any egg masses on the trees, including those of praying mantids and Gypsy moth, should also be removed.
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. Insects occurring on the tree should be left there until the tree is removed. Any that collect on ceilings, walls, or windows can be eliminated with a vacuum cleaner. It is important to remember that these “critters” are normally found outdoors, on LIVE trees. Warm temperatures, low humidities and lack of appropriate food conditions typical of most homes will usually 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.
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, apidlike, 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, are harmless.
Occasionally, aphids will hatch from Christmas trees in sufficient numbers to cause alarm. Most aphids are tiny, inactive, and usually go unnoticed. Aphids of the genus Cinara, however, reach a length of nearly 1/8 inch, making them one of the largest of our native aphids. Most forms, especially those of early generations, are wingless and remain active throughout their lives. If your Christmas tree remains indoors for an extended period (particularly if it is a live tree) these aphids may produce offspring, and winged forms may occur.
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 twigs aphid may occur. This gray-green species is much smaller than the spiderlike 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, i.e., they can only survive by feeding on certain plants. They will not feed on your houseplants.
Several species of minute, dark brown to black beetles may be found on or near the tree. They may be boring into the trunk, creating small holes and very fine sawdust. These are bark beetles that were overwintering in the tree. Although they bore into bark or wood, they are not a threat to any of the furnishings or structural parts of the house because wood inside the home is too dry for these beetles to survive. When the tree is removed at the end of the holiday season, the bark beetles will again go into dormancy, resuming their normal activity in spring.
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 in the adult state 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.
These large, showy insects overwinter in egg masses that are frequently attached to conifer limbs. These eggs will begin to hatch after being indoors for several weeks. When this happens, numerous tiny mantids swarm over the tree seeking food. Since they are cannibalistic they will eat each other if no other food is available.
The popular misconception that these beneficial insects are protected by law may prompt people to attempt to keep praying mantids alive until they can be released outdoors. None of the mantids are protected and keeping them alive in captivity is impossible, given the voracious appetite of a growing mantid. Also, if released outdoors when temperatures warm in early spring, survivors would quickly die, since their life cycle would not be synchronized with their prey.
It is best to look for the light tan, walnut-sized, frothy egg masses on the tree before it is taken indoors. Cut out any small twig with an attached egg mass and place it in an evergreen shrub or tree outdoors. In spring, eggs will hatch and the mantids will have appropriate food available.
These insects are sometimes, unfortunately, referred to as “barklice,” a name that is misleading since there is nothing louselike about them. Psocids are small, winged, soft-bodied insects colored gray or brown. “Barklice” 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 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.