Wood beetles are a diverse group of insects whose young, known as larvae, feed on the structural components of wood. These wood-boring insects belong to various families within the order Coleoptera, or beetles. Identifying a specific wood beetle can be challenging due to the vast number of species. Identification relies on observing the insect’s appearance at various life stages and the specific damage they leave behind.
General Appearance of the Adult Wood Beetle
The adult wood beetle shares common traits with other beetles, featuring a hard, protective outer shell. This hardened forewing, called the elytra, covers the delicate hindwings and most of the abdomen. Adult size varies significantly, ranging from tiny specimens as small as 1/12 of an inch up to robust individuals exceeding two inches in length.
Their body shapes are typically elongated and cylindrical, oval, or bullet-shaped. Coloration is highly variable, usually falling within shades of brown, reddish-brown, or black. Some species, like metallic wood borers, exhibit a striking, iridescent sheen of blue, green, or coppery-brown. The adult form is the reproductive stage; its main purpose is to emerge from the wood, mate, and lay eggs. Many adults are strong fliers and may be found near windows or light sources after emerging. Finding a dead adult beetle is often the first clue of an infestation.
The Destructive Larval Stage
The larva, commonly called “woodworms,” is the life stage responsible for nearly all wood damage. Larvae look completely different from adults, lacking the hard shell and defined beetle shape. They are soft-bodied, segmented, and appear pale white or cream-colored.
Wood beetle larvae are often C-shaped and have a fleshy, grub-like appearance. They possess a distinct, hardened head capsule that is usually a darker brown or yellowish color. Powerful mandibles, or jaws, are located on the head and are used to chew through wood fibers as they tunnel. Larvae remain hidden inside the wood for the majority of their lifespan, which can last from several months to many years depending on the species. They feed on the starches and cellulose, creating tunnels that widen as they grow.
Key Differences Among Common Wood Beetle Families
The appearance of the adult insect is the best way to differentiate between major wood-boring beetle families.
Powderpost Beetles
Powderpost beetles, including Lyctids and Anobiids, are small, measuring between 1/12 and 1/4 inch long. True powderpost beetles (Lyctids) are slender with a prominent head. The common furniture beetle (an Anobiid) has a hooded segment behind the head, giving it a humpbacked appearance that conceals the head when viewed from above.
Long-horned Beetles
Long-horned beetles (Cerambycidae) are significantly larger and more robust, with some species reaching up to two inches. Their most distinguishing feature is their long antennae, which can be as long as or longer than their entire body. The old house borer, a well-known long-horned beetle, attacks softwoods and often has a brownish-black body with patches of grayish hair.
Deathwatch Beetles
Deathwatch beetles, also part of the Anobiidae family, are oval and typically reddish-brown to black. Some species are covered in fine, pale hairs, giving them a dusty or mottled appearance. These beetles are known for a ticking or tapping sound they make by striking their head against the tunnel wall, a mating signal often heard in quiet environments.
Identifying Visual Evidence of an Infestation
Most people discover an infestation by finding the evidence the beetles leave behind rather than the insects themselves. The most common sign is the presence of small, circular exit holes in the wood surface, which adults chew to emerge. The size of these holes strongly indicates the species.
Exit Holes
True powderpost beetles create tiny pinholes, typically 1/32 to 1/16 inch in diameter. Deathwatch beetles leave slightly larger, round exit holes, usually measuring between 1/16 and 1/8 inch across. Long-horned beetles create the biggest holes, sometimes up to 1/4 inch or more in diameter, which may appear slightly oval. New exit holes have clean, sharp edges, while older holes may be discolored or filled with paint.
Frass (Wood Dust)
The second key piece of evidence is frass, the fine, powdery material pushed out of the exit holes. True powderpost beetles produce frass that is extremely fine and feels like talc or flour. Deathwatch beetle frass is coarser, feeling gritty, and may contain small, bun-shaped pellets. Long-horned beetle frass is often barrel-shaped and more coarsely packed, sometimes resembling sawdust.