E-394 03/06

Structure-Infesting Wood-Boring Beetles John A. Jackman*

everal kinds of beetles damage stored wood-boring insect; it is usually mixed with wood, structural timbers and other excrement. The beetles push the frass from the S wood products. The tunneling activities holes they have made in the infested wood. This of the larvae and the emergence of adults can frass usually gets piled below the holes or in weaken wood and may destroy its appearance. cracks in structures. The consistency of the frass Wood-boring beetles come from at least 12 ranges from very fine to coarse, depending on insect families and vary greatly in size, wood the species. preference, nature of damage and other habits. Sometimes an infestation is indicated by the Although preventing beetle infestations is desir- presence of wood-boring beetle adults. Adult able, control measures are available if infesta- beetles that emerge in confined structures are tions are found. To control wood-boring beetles, attracted to lights or windows and may accumu- it is extremely important that the beetles or late at these locations. beetle damage be identified properly, as control Other signs of an infestation include stained measures vary by species. wood or a blistering appearance on the wood Other insects also attack and damage wood, surface caused by larvae tunneling just below including termites, carpenter ants and carpenter the surface. Less commonly, immature beetles bees. Their appearance and damage characteris- produce audible rasping or ticking sounds while tics vary greatly. chewing on the wood. These chewing sounds are most often heard during quiet times at night. Detection There are several indicators that wood-boring beetles are present. Probably the most common sign of a wood-boring beetle infestation is the presence of holes chewed by the adult beetles upon emergence. Another indicator is a powdery material called frass that beetles often produce while feeding. Frass is plant fragments made by a

*Professor and Extension Entomologist, The Texas A&M Powderpost beetle tunneling. University System Identification If you discover beetle adults, beetle larvae or other evidence of an infestation, obtain a correct identification of the beetle family or species involved. Identification is important to make informed decisions about whether the Adult beetles are likely to continue to attack the wood 1 to 35 days in your home and whether treatment is justified. Flying, mating, egg laying Egg Adult wood-boring beetles range from under 1 to 4 weeks 1 ⁄8 inch to more than 2 inches long. Although Laid on or in wood many are dark colored, some are metallic blues, metallic greens or striped with yellow or red. If you find only adults, try to find any emergence holes or damaged wood, which identifies the area infested. Immature wood-boring beetles usually re- main inside the wood and therefore are seldom Pupa 1 to 4 weeks seen. These grubs are typically soft and fleshy, Change from larva to adult Larva 1 white to cream-colored with a distinct head cap- occurs near wood surface 1 ⁄2 months to 12 years sule that is brownish. The size varies from very Feeding within wood tiny just after hatching to more than 2 inches Typical wood-boring beetle life cycle. long. The bodies are noticeably segmented and elongate. They may be cylindrical or flattened. Knowing the kind of wood—hardwood or live in wood as larvae for up to 30 years before softwood—can help you identify the beetle spe- emerging as adults. This complicates detection cies involved. Sometimes wood-boring beetles and control because it is difficult to assess the enter homes accidentally because they are length of time an infestation has been present. attracted by lights; in these cases, they almost The variation in biology for these beetles is out- never damage property. More often, beetle lined in Table 1. infestations arise from the use of infested wood The emergence holes of wood-boring beetles during the construction of the house. are usually round, but some species produce semicircular or oval holes. The shape and size of the emergence holes can help identify beetle Biology and habits groups. Wood-boring beetles have four life stages: The type and location of frass is also charac- egg, larva, pupa and adult. The eggs and pupae teristic of various beetle groups. Notice whether do not feed. Larvae, or grubs, are the main dam- it is packed into the tunnels or extruded through aging stage, but the adults of some species can exit holes. Also, note its texture (powdery, pellet- also damage wood. ized, coarse or shredded). All these characteris- Most types of wood-boring beetles do not tics can help identify beetles when no specimen damage seasoned structural timbers or finished is available. A hand lens is often helpful to deter- wood products. However, if infested wood is mine the frass characteristics of wood-infesting used in construction, beetles can emerge from beetles. structural timber, doors, flooring, molding or Often, various beetle groups can be recog- paneling. nized and control measures planned based on The length of the life cycle (egg to adult knowledge of their wood preferences. Table 2 stage) of wood-boring beetles varies greatly summarizes the types of wood attacked, the among species and under different environmen- usual damage or emergence sites in buildings tal conditions. Some beetles complete a life cycle and reinfestation capabilities. This table should within a few months; others have been known to help in planning appropriate control measures. For instance, the lyctid powderpost beetles attack only seasoned hardwoods, and they are serious pests when they do. Thus, lyctid powder- post beetles found in hardwood floors, wood trim, or furniture would not be expected to at- tack softwood such as pine timbers in a home. On the other hand, deathwatch beetles attack Powderpost larva both softwoods and hardwoods, and they gener- (3-5 mm) Typical length of powderpost beetle adult (4-6 mm) ally feed on seasoned wood.

Table 1. Biological characteristics of wood destroying beetles. Group Exit hole Destructive Typical length Types of frass Diameter Shape stage of life cycle

1 1 Lyctidae ⁄32 to ⁄16 inch Round Larva 3 months Flour or talc-like; readily pours (Powderpost beetles) to 1 year out of exit holes and cracks

1 1 Anobidae ⁄16 to ⁄8 inch Round Larva 1 to 3 years Fine to coarse; pellet shapes; (Deathwatch beetles) usually a gritty quality; loose in tunnels; little at exit holes

1 3 Bostrichidae ⁄8 to ⁄8 inch Round Larva Usually 1 year Fine to coarse; tightly packed; (False powderpost beetles) and adult tends to stick together

1 1 Ptinidae ⁄16 to ⁄12 inch Round Larva Several months Fine and powdery; fills larval (Spider beetles) under favorable tunnels conditions

1 1 Curculionidae ⁄32 to ⁄16 inch Round Larva Varies with species Powdery or granular dusts (Weevils, snout beetles) and adult packed in irregular tunnels

1 1 Buprestidae ⁄32 to ⁄2 inch Oval Larva 1 to 30 years None at exit holes; coarse (Flatheaded borers) powder in tunnels

1 Oedemeridae ⁄4 inch Round Larva About 1 year Shredded and moist (Wharf borer)

Cerambycidae (Roundheaded borers) 1 1. Old house borer ⁄4 inch Oval Larva 1 to 32 years Tunnels filled with powdery (normally 3 to 10) dust often formed in pellets

1 1 2. Flat oak borer ⁄16 to ⁄12 inch Slightly Larva 1 to several years Tunnels packed with fine oval flourlike dust and granules

1 1 3. Other roundheaded ⁄8 to ⁄2 inch Round Larva Variable Coarse and fibery in tunnels borers

Scolytidae Less than Round Adult and 2 months to Little or none at exit holes; 1 (Bark beetles) ⁄16 inch larva 1 year or more very little or none in tunnels

Brentidae, Less than Round Larva Unknown; Galleries free of frass and not 1 1 Lymexylidae, ⁄32 to ⁄8 inch probably stained and Tenebrionidae several years (Timber worms) One of the most sig- Because other beetle groups do not reinfest nificant wood infesting structural timbers, controlling them may be un- beetles is the old house necessary. Most flatheaded borers, roundheaded Old house borer larva borer, which is a mem- wood borers and bark beetles are found shortly ber of the roundheaded after a structure is built. Adults of these species wood borer family. It generally will emerge within a few years after a generally attacks struc- building has been constructed. These beetles do tural softwoods. Con- not normally reinfest seasoned structural wood. trary to its name, it is often a pest in newer homes built with infested Prevention wood. Wood becomes Prevention is the best way to avoid damage susceptible to attack if it caused by wood-boring beetles. Several standard is improperly kiln-dried procedures are available to eliminate or avoid or treated, or stored too these problems. long. This insect will Some management efforts start when the Typical length of old house readily reinfest structural wood is harvested. Timber should have the bark borer adults (12-18 mm) timbers. removed soon after it is felled, to inhibit egg

Table 2. Attack sites of wood-destroying beetles. Timbers attacked Wood stage attack Adult emergence sites Reinfestation and damage in buildings

Unseasoned Seasoned Softwood Hardwood Sapwood Heartwood trees Living Dying trees or recently felled logs Seasoned lumber products and wood and/or Woodwork flooring timbers Structural Furniture, tool handles, etc. Firewood

Powderpost beetles X X X X X X X X Yes

Death watch beetles X X X X X X X X X X * Yes

False powderpost beetles X X X X X X X X X X X Rarely

Spider beetles X X X X X X X No

Snout beetles X X X X X X X X X X X Yes

Flatheaded borers X * X X X X X X * X X * X No

Wharf borer X X X X X Yes

Roundheaded borers 1. Old house borer X X X X X X Yes

2. Flat oak borer X X X X X X No

3. Other roundheaded X X X X X X X X X X * X No borers

Bark beetles X ** X X X X X X * X X X No

Timber worms X X X X X No *Possible **Rarely Store firewood as far from the home as pos- sible or at least stack it away from the outer walls. Bring in only the wood that will be used immediately. Before buying, carefully inspect antique furniture, picture frames, bamboo products and other wood items. Consider the wood to be ac- tively infested if you see any evidence of recent emergence holes, larval infestations or frass. Treat these items properly before placing them in your home or in storage. Control Powderpost beetle damage. Several options are available for controlling wood-boring beetles. First, try to identify the specific beetle or beetle group involved. Once laying of wood-boring beetles. Lumber should be recognized, determine the extent of the damage removed from the forest as quickly as possible and evaluate the structural characteristics of the and allowed to dry. Kiln drying of lumber will infested building. This information will help you kill beetles infesting the wood. However, because determine a proper plan for any control efforts. kiln drying has no lasting effects, reinfestation is The most common methods used to control possible in some situations. wood-infesting beetles include replacement of Before buying wood, evaluate it closely by infested wood, temperature treatment of the inspecting it for exit holes or other signs of wood, surface treatment with insecticides, or fu- infestation. Buy and use only structural wood migation. If the infestation is localized, replacing and wood trim that has been properly kiln-dried infested wood is often a good choice. Remove or or chemically treated. Proper kiln-drying will replace structural wood or furniture whenever it eliminate any infestation. However, infestations is economically feasible. Replacement reduces the may still occur in wood that is stored after be- risk of spread or reinfestation and eliminates any ing kiln-dried. Wood that is treated chemically unsightly damage visible in the finished structure. in pressure chambers will resist infestation for It is difficult to treat an entire structure for many years. wood-boring beetles with heat or cold. However, Control moisture in the home or structure. it is feasible to treat small home furnishings, Moisture-control options include repairing leaks wooden artifacts or furniture by freezing or heat- and installing vapor barriers, insulation, dehu- ing them to eliminate wood-boring beetles. To midifiers and air conditioners. Most wood-in- freeze wood-boring beetle larvae, maintain the festing beetles cannot develop in wood that has wooden items at about 0 degrees F for several a moisture content of less than 15 percent. Low weeks to eliminate an infestation, because many moisture will also help prevent decay, which can wood-boring beetles are resistant to cold tem- aggravate wood-boring beetle problems. peratures. Maintain a fresh coat of paint or varnish Alternately, heat can kill insects in wood by on all furniture or exposed wood in your home. maintaining the wood at temperatures of 140 to Most wood-boring beetle species will not reinfest 150 degrees F for 2 to 4 hours. However, wood wood that is painted, varnished, waxed or cov- thicker than 2 inches may take a long time to ered with some other type of finished surface. heat internally, so expect to hold the wood much Avoid introducing new sources of wood-boring longer at appropriate temperatures. Be aware beetles, such as firewood. Adult beetles and vari- that surface temperatures of wood seldom reflect ous other pests can emerge from wood temporar- the internal temperature. Extremely high tem- ily stored in the home and then infest structural peratures probably help reduce beetle infesta- wood or furniture or become a nuisance. tions in many attics. Pesticide treatments for wood-boring beetles Bor® and Bora-Care®. These products are best are best done by a licensed pest control opera- used on freshly installed wood before completion tor. A localized infestation may be treated by of home construction. Applications are typically spraying or brushing a residual insecticide on the made as a water emulsion applied twice, the sec- wood surface. ond time before the first application dries com- Depending on the product used, the insec- pletely. Applications to unfinished wood surfaces ticide may stay near the surface or penetrate will allow some penetration into the wood. deeper. Insecticides that stay near the surface af- However, many types of wood finishes— fect only the adults that emerge from the wood paint, varnish, wax—do not permit insecticide or attempts to reinfest the wood. Larval develop- penetration. Also, outdoor structures or wood ment beneath the wood surface often continues. surfaces that are exposed to moisture are poor Surface treatments that do not penetrate gener- candidates for treatment with borates because ally do not control infestations of wood-boring of leaching. Water exposure tends to draw out beetles that bore deeply into the wood. Some of soluble compounds, rendering the treatments those, such as the old house borer, have adults less effective over time. that can mate and produce eggs without leaving The most reliable and effective method of their larval tunnels. eliminating wood-boring beetles is fumigation. Products containing beta-cyfluthrin (Bayer® Fumigation involves introducing a toxic gas into Power Force Carpenter Ant & Termite Killer a structure, usually under a gas-proof tarp. The Plus), bifenthrin (Ortho® Termite & Carpenter fumigant gas penetrates beneath the wood’s sur- Ant Killer), and cyfluthrin (Bayer® Advanced® face to kill all life stages of the beetle. Home, Home Pest Control Indoor & Outdoor Fumigation does not prevent subsequent re- Insect Killer) are registered for homeowners to infestation. Because it is a costly, highly techni- use to control wood-boring beetles. Several other cal and hazardous process, fumigation must be products containing those active ingredients, done by a licensed pest control operators experi- or others such as cypermethrin, deltamethrin, enced with this technique. fenvalerate, imidacloprid and lambda-cyhalo- thrin, are available to pest control operators. Insecticide label clearances are subject to Because surface treatments with these products change and changes may have occurred since do not penetrate the wood very well, they are this publication was printed. The pesticide user used primarily to prevent the next generation is always responsible for the effects of pesticides of wood-boring beetles from establishing in the on his own plants or household goods as well as wood. problems caused by drift from his property to Wood penetrating treatments are possible other property or plants. Always read and follow with water-soluble borate products such as Tim- carefully the instructions on the container label.

A previous version of this publication was written by J. A. Jackman and P. J. Hamman.

Revision