Adult, Larva
| Common Name | Scientific Name |
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| Old House Borer | Hylotrupes bajulus (L.) |
Larvae of the old house borer feed on seasoned softwoods and prefer the sapwood portions of pine, spruce and fir. Sometimes larvae are serious pests in modern log homes as well as conventional homes. Houses less than 10 years old are primarily attacked contrary to the name of old house borer. Full grown larvae can be heard boring in the wood, making a rhythmic ticking or rasping sound much like the sound of a mouse gnawing. In log houses, this sound may be heard from a distance of five to ten feet, day and night, at infrequent intervals. If the larvae work close to the surface, homeowners may find blistering of the wood, boring dust on surfaces below infested timbers, powdery borings in sapwood, oval emergence holes about 1/4 inch wide on the wood surface, larvae in tunnels or beetles in the building.
Adult old house borers are beetles 5/8 to 1 inch long, slightly flattened, brownish-black with many gray hairs on the head and thorax, two prominent black bumps on the prothorax and long antennae. The thorax (segment behind the head) has a shiny ridge down the middle and a shiny raised knob on each side, appearing as a face with a pair of eyes. Wing covers are marked with whitish spots that form two irregular bands or spots near the middle. Larvae are up to 1-1/4 inches long and have tiny ocelli (black eye spots) on each side of the head. They are flesh-colored, wedge-shaped (wider at the head), and segmented with legs present. Pupae are flesh-colored and about the size of the beetle. Eggs are white to grayish-white.
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| Old House Borer Adult, Larva |
The biology of the beetle's life cycle is greatly influenced by temperature, relative humidity and protein content of the wood. In Virginia, larvae require two to ten years to become fully grown and their feeding can cause extensive damage to infested wood. The adult stage is short, lasting eight to sixteen days, the egg stage about two weeks, the larval stage several years and the pupal stage two weeks. Under ideal conditions in many southern states, adults may appear after three to five years, sometimes remaining in larval tunnels for as long as 10 months before emergence. In more northern states, where humidity is low (as in some attics), an additional two to five years may be required to complete the life cycle. Adults emerge June, July and August with females attracted to dry, seasoned wood where eggs are laid reinfesting additional softwood. (Oils and resins in the heartwood portion of wood are undesirable.)
Log houses have become quite popular in many states. Many are made from pine trees (southern yellow pine and red pine), usually cut near the manufacturing site. Logs are partly or completely debarked before being cut into lengths and notched as part of a log house kit. These logs are strapped together and dipped into a preservative with the kit completed in a few days or weeks. Logs remain outdoors at the manufacturing site until the kit is complete. Then the entire house kit may be fumigated, loaded onto trucks and delivered to the construction site where logs may sit again before the homeowner assembles the house. The flight period of adult old house borers (June, July, August) may coincide at the manufacturing site or delivery site. If a log house kit produced during the fall is delivered to the building site, but assembly not made until spring or summer, any eggs laid in the cracks and crevices of the logs will hatch in only about nine days with the first stage larvae immediately penetrating the wood. Larvae may have gone below the depth of preservative treatment before being dipped. In about two years (four to five years in conventional lumber) larvae can be heard feeding below the log surface. Adult emergence holes are discovered easily. Reinfestation of log houses seems greater than conventional houses because of more exposed wood and the shorter feeding time of larvae.
Homeowners often ask when and where the logs became infested. However, it is impossible to determine precisely. One needs to know when the log house was manufactured, when it was delivered, when it was assembled, and when larvae were first heard feeding in the wood. To suspect that the infestation originated at the manufacturing site, all or part of the log house kit needed to be produced during the flight period of the female beetles. The larval feeding sounds and size of larvae removed from wood are helpful clues. Infestations may occur at the construction site when the kit remains unassembled. Infestations are known from Maine south to Florida and west to Michigan to Texas. The westward range extends approximately to the Mississippi River.
Infestations are hard to detect in the early stages since larvae are small, develop slowly the first year and there are no external signs of damage. Only in advanced stages will surface bulges become evident due to larval activity. Homeowners may hear their gnawing "clicking-like" sounds. By breaking the surface with a sharp object where tunneling is suspected, one can find tiny rod-like fecal pellets (which crumble easily) and fine, powdery material. Sometimes mines are filled loosely with granular frass, some of which may fall out and reveal the borer's presence. The best characteristic is the striking size and cross-sectional shape of the galleries. Walls of these large oval galleries have a rippled appearance and, at their broadest dimension, larval tunnels may be 3/8 inch wide. The flight exit holes are oval-shaped, slightly flattened, corresponding to the adult beetle shape. Exit holes may be surrounded by small piles of frass and tiny pellets. Infested wood may have extensive damage, reducing the total sapwood area to a powdery frass with the outer veneer of wood left paper-thin. Materials attacked may include attic framing, floor joists, wood framing, trim, flooring, etc.
Damage depends on several factors. If the house is heated centrally, has no moisture problems from ventilation or poor drainage and does not stay closed up and unoccupied for long periods of time, infestations do not worsen significantly and reinfestations are unlikely after the first generation. It is sometimes common for a few boards in the house to be infested, resulting in very little economic damage in spite of a gnawing nuisance by a few larvae and occasional emergence by a beetle or two. However, in portions of the house with a high enough humidity to allow reinfestation, serious damage can result. Moisture contents below 10 percent cause very slow larval development and some die. Ideal development is at moisture contents of 15 to 25 percent. Larvae will even attack wood that has been air dried or kiln dried to about 25 percent moisture content. They do not infest firewood or any softwood not seasoned to some degree. The majority of infestations originate in wood containing larvae prior to construction. Larvae and adults have been found in lumberyards where structural and log-home timber were cut, dried and stored. The extent of damage depends on the proportion of sapwood to heartwood. With heating inadequate to dry out the framing timbers and high moisture present, such as in unheated storage areas or recreational structures occupied intermittently, serious damage can occur. Avoid using farm-sawed lumber of freshly cut logs unless chemical treatment has been applied.
Treatment involves the application of liquid insecticides to the surface of infested wood or the use of fumigants to treat the entire structure. The choice depends on the degree of infestation and whether immediate control is desired. Surface treatment is best just prior to adult emergence (June) to prevent reinfestation by killing the adult beetle. Most chemicals do not penetrate deep enough into the wood to kill the larval stage nor do larvae feed on treated wood. These localized infestations may be treated with spray or paintbrush applications of chlorpyrifos (Dursban) in oil or water, according to the label. The licensed pest control operator or applicator may use a lindane treatment. They can drill into infested timbers and introduce chemicals under pressure to force the toxicant throughout the gallery system. It may take a few months to a year to see results such as reduced chewing sounds, etc. Whole-house fumigation is a last resort where the infestations are active, widespread, damage is significant and an immediate end to the chewing sounds is desired. Fumigation kills all stages of the old house borer in the wood. In log houses the amount of fumigant used and amount of time the chemical is held in the structure may have to be increased due to the moisture content of the logs and their greater width compared to a conventional house. Only the licensed pest control operator or applicator can apply fumigants. The process requires several days of the structure being covered with gas-proof tarpaulins. Fumigation will not leave any residual chemical on the wood surface to prevent subsequent reinfestation. Be sure to replace or repair any serious structural defects caused by extensive borer feeding.
More recently, wood destroying borers can be treated with borates. Borates are environmentallty sound, odorless, non-flammable, low mamalian toxicity, not absorbed through skin contact, washes off easy with soap and water, readily absorbed into wood and can be used in homes with children and pets. The borates: disodium octaborate tetrahydrate (Bora-Care) 40% and (TIM-BOR) 98% are labelled. Bora-Care can be applied by homeowners, whereas TIM-BOR is labeled for pest control operator use only. It is usually best to employ the services of a licensed pest control operator or applicator since homeowners seldom have the training, experience or equipment to do the job thoroughly. Insecticides labelled for pest control operator use only include cyfluthrin (Tempo), cypermethrin (Demon TC), permethrin (Dragnet, Flee) and chlorpyrifos (Dursban TC, Equity, Tenure). Always read the insecticide label and follow directions and safety precautions.
This publication contains pesticide recommendations that are subject to change at any time. These recommendations are provided only as a guide. It is always the pesticide applicator's responsibility, by law, to read and follow all current label directions for the specific pesticide being used. Due to constantly changing labels and product registration, some of the recommendations given in this writing may no longer be legal by the time you read them. If any information in these recommendations disagrees with the label, the recommendation must be disregarded. No endorsement is intended for products mentioned, nor is criticism meant for products not mentioned. The author, The Ohio State University and Ohio State University Extension assume no liability resulting from the use of these recommendations.
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