Blackhorned Pine Borer
Fact Sheet No. 12
Dr. Jay B Karren, Extension Entomologist
Revised June 2003
Alan H. Roe, Insect Diagnostician
Identification
The blackhorned pine borer, Callidium antennatum hesperum Casey, is a member of the
family Cerambycidae. These beetles are commonly called long-horned beetles because of
their long antennae. The larvae are usually called round- headed borers, and all but a few
members of the family live in the tissues of trees or other woody plants. These beetles are
common species in western forests, attacking boles and limbs of dead or dying pine,
Douglas-fir, and mountain hemlock.
The adult is flattened, bright metallic blue, violet or bluish- black, and from 3/8 to 1/2 inch
long. The males' antennae are somewhat shorter than the body; the thorax is rounded with
depressions on each side of the middle, and the legs are black with large femora.
Damage
Adults appear in early spring and fly to host material where they deposit eggs beneath bark
scales on dead trees or on cut wood that has seasoned over winter. The larvae feed in the
phloem and outer sapwood making broad, meandering, intertwined tunnels in the wood and
pushing large quantities of frass through small holes in the bark. Pupation occurs in the wood
in long cells plugged with wads of fibrous frass. There is usually one generation per year.
They generally will not attack a healthy tree but are attracted to dead, dying, diseased, or
stressed trees. Consequently, one of the control recommendations is to keep the tree in good
condition by pruning out damaged wood and maintaining good cultural practices such as
proper watering and fertilization. Young trees should be wrapped from the soil surface up to
the first large limb to prevent sunburn and later borer attack.
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This species frequently causes serious losses to improperly- edged lumber in lumber yards.
Rustic work and houses built of pine logs are also subject to serious damage, the wood being
badly riddled and weakened and the bark so loosened that it falls away. Prompt utilization of
logs, the removal of wane on cut lumber, and kiln drying are recommended methods of
control.
Control in Firewood
This insect is also one of the species that emerges from infested firewood brought into the
home. When the wood is brought into a heated structure it "fools" the biological clock of the
beetle into "thinking" it is spring and causes the beetle to emerge early. Under these
circumstances, emergence can occur anytime during the winter or spring. Many homeowners
are alarmed by the sudden appearance of these beetles. In the home they are merely a
nuisance. They will not harm people, pets, or structures. They will only infest host material
with the bark still attached and will not damage finished lumber. About the worst thing they
can do is mate and reinfest the firewood.
Once adult beetles emerge in the home, the simplest control measure is to merely swat them
with a fly swatter, sweep them up, and throw them outdoors or in the trash. Another option is
to collect the insects with a vacuum cleaner. They can also be killed by spraying them
directly with household insecticides labeled for control of flying and crawling insects. These
include various formulations of ready-to-use solutions and pressurized liquids. Active
ingredients in such products include eugenol, permethrin, phenothrin, pyrethrins, resmethrin,
and tetramethrin. These materials are expensive, generally leave an odor, and usually are not
required for the number of beetles that have to be dealt with. If firewood is found to be
infested, you can greatly reduce the number of beetles that emerge in the home by leaving
the wood outdoors until you are ready to burn it.
Firewood piles may be repeatedly infested by these beetles until the wood dries out to the
point that it is no longer attractive for oviposition. One method to prevent reinfestation is to
debark the wood, but this is difficult and time consuming. Storing the wood under clear
plastic tarps has produced mixed results. If done properly, with the edges of the tarp sealed
by piling soil on top of them, the temperature in the wood pile may rise high enough to kill
the borers. You may experience some problems with condensation and mold growth on the
wood with this method. Black plastic is not recommended because the beetles can detect
light coming through pinholes in the plastic, congregate at the holes, and chew their way out.
Spraying the firewood with insecticides is generally not recommended because multiple
applications would be required and all bark-covered surfaces of the wood would have to be
sprayed to offer complete protection. This usually isn't practical in large wood piles, and it is
easier to use up small wood piles than it is to treat them.
Precautionary Statement
All pesticides have both benefits and risks. Benefits can be maximized and risks minimized
by reading and following the labeling. Pay close attention to the directions for use and the
precautionary statements. The information on pesticide labels contains both instructions and
limitations. Pesticide labels are legal documents, and it is a violation of both federal and state
laws to use a pesticide inconsistent with its labeling. The pesticide applicator is legally
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