Wood Boring Beetles

Wood Boring Beetle Identification Guide

Wood boring beetles are among the most destructive insect pests that can affect homes. Unlike termites that maintain contact with soil, these beetles complete their entire lifecycle within wood. The larvae do all the damage, tunneling through lumber for months or even years before emerging as adults through small exit holes.

Physical Characteristics

Adult wood boring beetles range widely in size depending on species. Small powderpost beetles measure just 2-7mm, while old house borers can reach 25mm. Most have elongated, cylindrical bodies well-suited for entering wood. Colors range from reddish-brown to dark brown or black.

Key identification features include:

• Elongated or oval body shape
• Hard wing covers (elytra) that meet in a straight line down the back
• Antennae that vary by species (short and clubbed or long and segmented)
• Six legs with small claws for gripping wood surfaces

The larvae look very different from adults. They are cream-colored, C-shaped grubs with visible head capsules. Larval size depends on species and age, ranging from tiny hatchlings to grubs over 30mm long in old house borers.

Common Species in North America

Powderpost Beetles (Lyctidae family) are the most common wood borers found in homes. Adults are small (2-7mm), slender, and reddish-brown to dark brown. They attack only hardwoods like oak, ash, hickory, and walnut. The frass they produce is extremely fine, like talcum powder. These beetles often infest hardwood flooring, furniture, and trim.

Old House Borers (Hylotrupes bajulus) belong to the longhorn beetle family (Cerambycidae). Adults are larger (15-25mm) with grayish-black bodies and distinctive white markings. They have long antennae. These beetles attack softwood lumber, particularly pine, spruce, and fir used in home framing. Larvae can feed for 3-15 years before emerging.

Furniture Beetles (Anobium punctatum) are small (3-5mm), reddish-brown beetles with a distinctive hood-like projection covering their head. Also called “woodworm” in Europe, they attack both hardwoods and softwoods. Their frass is gritty rather than powdery. They prefer wood with some moisture content and often infest furniture, structural timbers, and antiques.

False Powderpost Beetles (Bostrichidae family) resemble true powderpost beetles but are larger and have a more cylindrical body. The head is hidden when viewed from above. They attack both hardwoods and bamboo. Unlike other species, adult bostrichids also bore into wood to lay eggs.

Wood Boring Beetle Behavior and Biology

Lifecycle and Development

All wood boring beetles go through complete metamorphosis with four life stages: egg, larva, pupa, and adult. Understanding this lifecycle is key to effective control.

Eggs are tiny, white, and deposited in cracks, pores, or existing exit holes in wood. Powderpost beetles lay eggs only in large-pored hardwoods because they cannot penetrate small wood pores. Furniture beetles prefer rougher wood surfaces. Eggs hatch in 1-3 weeks.

Larvae cause all the structural damage. After hatching, they tunnel into the wood and feed on cellulose and starches. Development time varies greatly by species and conditions. Powderpost beetle larvae mature in 9-12 months. Furniture beetle larvae take 1-3 years. Old house borer larvae can feed for 3-15 years in a single piece of wood.

Pupae form in chambers near the wood surface. This stage lasts 2-4 weeks. Pupae do not feed.

Adults chew their way out, creating the round exit holes that signal an infestation. Adults live only 2-6 weeks and do not damage wood. Their sole purpose is reproduction. Most species are attracted to light and may be found on windowsills.

What Attracts Wood Boring Beetles?

Different species have different preferences, but several factors increase infestation risk:

• Wood moisture content: Most species prefer wood with 10-30 percent moisture content. Very dry wood (below 6 percent) and properly kiln-dried lumber resist infestation.
• Wood type: Powderpost beetles attack hardwoods only. Old house borers prefer softwood framing. Furniture beetles infest both.
• Starch content: Larvae need starches and sugars in wood to develop. Older heartwood has less nutrition than sapwood.
• Existing exit holes: Some species reinfest wood through old exit holes.
• Poor ventilation: Damp crawlspaces and attics create ideal moisture conditions.

Signs of Infestation

Exit holes are the most obvious sign. Powderpost beetle holes are 1/32 to 1/16 inch diameter. Furniture beetle holes measure 1/16 to 1/8 inch. Old house borer holes are larger and oval, about 1/4 to 3/8 inch.

Frass (boring dust) accumulates below exit holes. Texture helps identify the species:

• Fine, talc-like powder: Powderpost beetles
• Gritty powder with small pellets: Furniture beetles
• Coarse, tightly packed material: Old house borers

Tunneling sounds can sometimes be heard in heavily infested wood. Old house borer larvae make clicking or rasping sounds as they feed.

Fresh vs. old damage: Active infestations produce light-colored, fresh-looking frass. If the powder is yellow or has settled into place, the infestation may be old or inactive.

Treatment Methods for Wood Boring Beetles

Assessment and Identification

Effective treatment starts with proper identification. Different beetle species require different approaches. A trained inspector will:

• Identify the beetle species from exit holes, frass, and any collected specimens
• Determine if the infestation is active or old
• Assess the extent of damage and affected areas
• Check moisture levels in affected wood
• Evaluate whether wood needs replacement or can be treated

Surface Treatments

For accessible wood with light infestations, surface treatments can be effective:

Borate treatments penetrate wood and kill larvae while providing lasting protection. Water-soluble borates (disodium octaborate tetrahydrate) are commonly used on unfinished wood. The treatment penetrates the surface and kills feeding larvae over time. Borate-treated wood also resists future infestations.

Residual insecticides applied to wood surfaces kill adult beetles as they emerge. This does not immediately eliminate larvae inside the wood but breaks the reproductive cycle over time. Multiple applications may be needed over 1-2 years.

Heat Treatment

Heating infested wood to 130-140 degrees Fahrenheit throughout kills all life stages. This method works well for:

• Individual furniture pieces
• Small areas of flooring
• Items that cannot be chemically treated

The entire piece must reach the target temperature at its core for at least 30 minutes. Professional heat chambers or localized heating equipment can achieve this.

Fumigation

For severe structural infestations or when beetles are in inaccessible areas, fumigation may be necessary:

• The entire structure is sealed and tented
• Fumigant gas (sulfuryl fluoride) penetrates all wood
• All life stages are eliminated
• No residual protection remains after treatment

Fumigation is costly and requires vacating the home but provides complete elimination when other methods cannot reach the infestation.

Wood Replacement

Heavily damaged structural wood may need replacement rather than treatment. Signs that replacement is needed include:

• Wood that crumbles or feels soft when probed
• Multiple generations of exit holes
• Visible tunneling throughout the wood
• Structural integrity concerns

Prevention Strategies

Preventing wood boring beetle infestations is easier than eliminating them:

• Use kiln-dried lumber for construction and repairs
• Inspect secondhand furniture and antiques before purchase
• Control moisture in crawlspaces and attics with proper ventilation
• Seal and finish wood with paint, varnish, or polyurethane to prevent egg-laying
• Do not store firewood indoors or against the house
• Remove old tree stumps and dead wood near your home

References and Further Reading

• University of Missouri Extension - Wood-Boring Beetles
• University of Florida IFAS - Powderpost Beetles and Wood-Infesting Insects
• Clemson University HGIC - Wood-Boring Beetles in Houses
• UC Davis IPM - Wood-Boring Beetles in Homes
• National Pesticide Information Center - Wood Boring Beetles
• NC State Extension - Powderpost Beetles and Wood-Inhabiting Fungi