Ohio State University Extension Fact Sheet

Ohio State University Extension Fact Sheet

Entomology

1991 Kenny Road, Columbus, OH 43210-1000


Firewood Insects

HYG-2065-96

Common Name Scientific Name
Roundheaded Borers Cerambycidae
Flatheaded Borers Buprestidae
Bark Beetles Scolytidae
Ambrosia Beetle Xyleborous sp.
Powderpost Beetles Lyctidae, Bostrichidae, Anobidae

Fireplaces and woodburning stoves have grown very popular over the past several years, creating a demand for firewood. Although wood, considered a renewable fuel resource, is relatively inexpensive, often readily available and can quickly warm a cold room, it can also serve as a home for certain nuisance insects and their relatives. Homeowners become alarmed when sawdust is pushed out of the firewood, faint rustling or gnawing noises are heard and insects emerge to crawl or fly within the house. For the most part, firewood insects are a nuisance by their presence and cause no harm to the home, household furnishings or humans.

Identification

Most insects and their relatives found in firewood are considered either woodboring or shelter seeking.

Insects that bore into wood include:

Roundheaded Borers (1/3 to 3 inches long)

The adults, also known as longhorned beetles, are attracted to dying, freshly cut or recently-killed trees. Eggs are laid in the bark crevices of the green (unseasoned) wood with larvae tunnelling throughout the wood for a year or longer. The amount of feeding depends on the wood moisture and surrounding temperature. After larvae pupate, adults emerge with large amounts of sawdust exuded from the circular exit holes (diameter of a pencil or larger.)

Painted hickory borer adults emerge during the spring (April & May) while locust borer adults are found during early autumn (September & October). Both resemble each other, but can be distinguished by emergence time. Locust borers feed on black locust whereas painted hickory borers feed on freshly cut hickory, osage-orange, hackberry, grape and ash. The redheaded ash borer attacks ash, oak, hickory, persimmon and hackberry. Other roundheaded borers found in Ohio include the ivorymarked beetle, elm borer, tanbark borer, and pine sawyer. Sometimes these large, multi-colored, strikingly-patterned beetles emerge in the home in January and February when firewood is stored indoors. (See, HYG-2127-94 for specific beetle descriptions.) Except for the old house borer, none of the other roundheaded borers will infest structural or interior wood in the house. Larvae of the old house borer feeds on seasoned softwoods, preferring pine, spruce and fir.

Flatheaded Borers (1/4 to 1-1/3 inches long)

The adults, also known as metallic wood borers, attack living, dying and weakened trees. Eggs are laid in the bark crevices with larvae tunnelling under the bark surface. After larvae pupate, adults emerge out of oval D-shaped exit holes.

In general, flatheaded borers attack fruit, shade and forest trees. The bronze birch borer prefers white or paper birches grown as shade and ornamental plants. None of the flatheaded borers will infest structural or interior wood in the house. Beetles are occasionally found indoors where birch logs have been used for decorative purposes.

Shothole Borer adult

Shothole Borer adult

Feeding Damage

Feeding Damage by the Shothole Borer

Bark Beetles (1/16 to 1/4 inch long)

Adults, also known as shot-hole borers, primarily attack dead and dying trees. Adults bore through the bark, forming galleries, grooving the surfaces of both the wood and the inner side of the bark. Eggs in the galleries hatch into larvae which feed in the cambium region. After larvae pupate, adults emerge through numerous small holes about the diameter of small lead shot.

Both the smaller European elm bark beetle and native elm bark beetle attack only elm trees and are important vectors, spreading the fungus ceratocystis ulmi known as Dutch elm disease. The shot-hole borer attacks peach, plum, cherry, apple, pear and related trees. Also, there are many pine bark beetles. They will not infest structural or interior wood in the house. If infested firewood is stored inside the home, beetles can emerge and become quite annoying by their presence. Many appear on windowpane surfaces.

Bark Beetle

Bark Beetle

Ambrosia Beetles (1/5 inch long)

Adults resemble bark beetles. They bore into the sapwood and often the heartwood, tunnelling in all directions. Tunnels, about pinhead width, are often stained black. They do not infest structural or interior wood.

Powderpost Beetles (3/32 to 1/3 inch long)

Adults can be found in dead wood as well as dried and seasoned lumber. Lyctid powderpost beetles attack hardwoods such as oak, ash, hickory and mahogany found in woodwork, flooring, structural wood, furniture, tool handles and firewood. Adults can emerge from firewood in the home and infest structural wood or furniture. Exit holes are about 1/32 to 1/16 inch in diameter. Flour or talc-like frass falls out of the exit holes and cracks. Anobiid powderpost beetles attack both hardwoods and softwoods. Most wood-infesting beetles will not reinfest wood that is painted, varnished, waxed or shellacked. Most beetles do not complete the life cycle in wood with a moisture content below 10 to 15 percent.

Brown Powderpost Beetle

Brown Powderpost Beetle

Feeding Damage

Feeding Damage by the Anobiid Powderpost Beetle

Carpenter Ant

Carpenter Ants and Termites

These insects can infest undisturbed piles of damp, unsound, wet firewood stacked on the ground outside. Infestations are usually not noticed until the stacked wood is moved. Infested wood may have concentrations either of ants or termite mud tunnels on the outside surface, especially where damp wood and high moisture conditions exist. Bringing in firewood infested with carpenter ants and termites usually will not result in infestations starting in the house. Both are social insects and the colony becomes so disturbed when the wood is moved, dried, cut or split that establishment indoors is very unlikely. Structural or interior wood should not become infested. However, wood stored in damp, moist basements or stacked on the ground outside against the house for several seasons should be avoided.

Carpenter Bees (3/4 to 1 inch long)

Adults resemble bumble bees, and bore round holes into outside wooden furniture, railings, fence posts, dead tree limbs and other weathered wood. Chances are slim of infesting structural or interior wood.

When firewood is stored directly on the ground, it absorbs and retains moisture within the wood, attracting a wide range of pests including sowbugs, pillbugs, millipedes, centipedes, spiders, bark lice (Psocids) and springtails. Other pests not as dependent on high moisture that may also use firewood as shelter include cockroaches, crickets, earwigs, flies and ground beetles. Sometimes yellowjacket wasps, paper wasps and bumble bees build nests in firewood piles presenting danger to those moving or stacking firewood. Their queens may overwinter under firewood bark and emerge early to fly within the house when wood is stored indoors under warm conditions.

Horntail Wasps (1 to 2 inches long)

Adults, also known as the Pigeon Tremex, sometimes emerge in the home causing excitement. Adults have a horny, spear-like long tail. Larvae burrow in maple, elm, beech and other trees. Structural or interior wood is not infested.

Pigeon Tremex

Pigeon Tremex

Pigeon Horntail adult

Pigeon Horntail adult

Insects and their relatives seeking shelter include:

Pennsylvania Woods Roaches (1/2 to 2 inches long)

Adults and nymphs live outdoors in hollow trees, under loose bark of dead trees, stumps, logs and in piles of firewood. These roaches are simply accidental hitchhikers into the house and cause no damage to structural wood, household furnishing or humans.

Pennsylvania Woodroach

Pennsylvania Woodroach

Darkling Beetles (1 inch long)

Adults that feed on bracket fungi are frequently found under loose bark where firewood has been stored outdoors on the ground for several seasons. Damp firewood held over several seasons outdoors usually becomes darkened and moldy. Considerable damage to firewood is caused by wood decay fungi, which send minute, fungal threads called "hyphaeż through the damp wood. Green, unseasoned wood is a prime target for decay fungi. Also, previously dry wood placed in contact with moist soil or in storage under high humidity conditions should be avoided.

Occasional Pests

Other pests occasionally found in firewood piles include spiders, woolyworm caterpillars and both mice and rats, which make their nests to rear young. Also snakes, which feed on insects and mice, may be discovered when moving sticks of firewood from the woodpile.

Life Cycle and Habits

Most firewood insects and their relatives are active from April to October. Many roundheaded and flatheaded borers complete their life cycle in one year or up to two to four years. Some adults prefer recently cut logs and others seasoned logs. Bark beetles and ambrosia beetles may have two to three generations per year and often attack weakened, dying and dead trees. Powderpost beetles complete their life cycle in three months to one year or up to three years with others living in the wood as long as 30 years before emergence. Powderpost beetles prefer wood that has been cut for several months (seasoned). Carpenter ants and termites prefer damp, moist wood such as old tree stumps and wood in soil contact. Carpenter ants can develop from egg to adult in about two months or up to 10 months in cooler weather.

Termite colonies vary in their life cycle with low populations the first year and active, larger colonies in the fourth year. (Termite establishment is slow depending on moisture, temperature and food.) There is one generation per year for carpenter bees and horntail wasps. The Pennsylvania woods roach life cycle is completed in one to two years, whereas certain darkling beetles require six months.

Control Measures

The most desirable firewood for heating includes ash, butternut hickory, white oak, American beech, red oak, sugar maple, cherry, white birch, rock elm, ironwood, locust, apple, dogwood, persimmon, yellow birch and black walnut. When seasoned (dried) properly, there is more heat per unit than unseasoned (green) wood and many insects are killed within.

Prevention

If possible, harvest living hardwood trees during the mid to late autumn months or early spring to allow some seasoning before winter and spring. At that time, wood borer beetles, primarily attracted by the smell of freshly cut, dying or decomposing trees, would be in the overwintering, inactive development stage. Trees cut during the summer months, (April through October) and left stacked in the woods, are very likely to become infested. Always remove logs from the forest or woods to reduce insect attack. The sooner the wood is split, the quicker it will dry and become less subject to insect infestations. Unsplit wood with the bark left on is very attractive to wood destroying insects and diseases. Firewood from dead trees is more likely to have bark beetle problems.

Never stack wood against the house or other buildings. Store firewood outdoors in an open area, as far away from the house as practical, to keep away insects and dirt (debris). Stack firewood off the ground to eliminate serious soil moisture problems leading to wood rot and pest problems. Stacking firewood in loose piles raised off the ground, as well as splitting or sawing into smaller sizes, accelerates drying. (This is needed with logs greater than eight inches in diameter and longer than four feet.) A simple storage rack can be made by placing two-by-fours on concrete blocks. Stack the firewood on top of the two-by-fours allowing an air gap of at least 10 inches between the ground and firewood.

For a cover, one can use a sheet of dark polyurethane plastic or sheet metal roofing to keep the wood dry. During the summertime, the area under the plastic will build up heat, evaporating the moisture and killing various stages of insects and other pests within. Provide proper ventilation if water vapor collects on the plastic cover from the green, unseasoned wood.

Bring only enough firewood into the house to be burned immediately. When cold weather arrives, pieces of firewood can be moved nearer to the house for easy access. Firewood should again be stored on a rack, patio or deck instead of on the ground. Firewood stored inside the home over an hour or so may warm up enough for insects to emerge from within or under the bark and start their spring activities early. Also, do not store firewood in a heated garage or basement for the same reason. Never store indoors over the summer.

Burn older wood first. Try not to carry over large quantities of firewood from season to season. After one to two seasons, unprotected firewood, left outside on the ground, will become tunnelled and full of frass from many woodboring insects, develop loose bark for nuisance insects to take shelter and decrease in heat value from wood decay fungi.

Piles of firewood should be inspected during the summer months for active pest populations and moved or restacked if practical and necessary.

Insecticides

It is best not to treat firewood with any pesticide. Spray treatments applied to the firewood will not kill woodborers within. Burning any insecticide-treated firewood indoors could cause a potential health hazard due to the toxic chemical fumes released into the living space by the burning wood.

If a colony of ants or beetles is found in a piece of firewood, it should be discarded outdoors away from the house, rather than burned or treated with insecticides. Any beetles or larvae appearing inside the house can simply be picked up with a vacuum cleaner, broom or dustpan and discarded.


All educational programs conducted by Ohio State University Extension are available to clientele on a nondiscriminatory basis without regard to race, color, creed, religion, sexual orientation, national origin, gender, age, disability or Vietnam-era veteran status.

Keith L. Smith, Associate Vice President for Ag. Adm. and Director, OSU Extension.

TDD No. 800-589-8292 (Ohio only) or 614-292-1868



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