Worms that bore holes in wood are actually beetle larvae, and occasionally, adult beetles. A variety of beetles of different sizes inflicts damage to wood. Generally, seasoned and finished wood is safe from the pests. However, beetles can emerge from finished products if they've had the chance to infest the wood.
According to Texas A & M University, there are at least 12 different families of insects represented among the wood-boring beetles. That means they range in size, as well as the type of wood they prefer to inhabit and the kind of damage they cause. When the offending beetle is in his wooden habitat, he'll chew his way through the wood, leaving "frass" -- a powdery substance of excrement and plant fragments -- in his wake. The type of hole the beetle makes, combined with the quality of the frass, provides clues about the type of insect doing the damage.
Long -- or Short -- Life Cycles
Beetles tend to do their damage during their larval stage, when they resemble worms. All beetles have four stages of life, moving from egg, to larva, to pupa to adulthood. The larva does most of the damage, but in some species, the adult can damage wood as well. The life cycle among the different species of wood-boring beetles varies widely. Some have a short lifespan of only a few months while others can live a year -- or even 30 years. This means a beetle can spend decades in a piece of wood before he emerges in his adult form. It also makes it difficult to find and control the insects because it's hard to know how long the larvae have been present in the wood.
Beetles on Borrowed Time
There are five species of beetles that take no more than a year to do their damage. Powderpost beetles live three months to a year and leave a talc-like frass behind in their wake. False powderpost beetles leave a round hole and a tightly packed frass that may be coarse or fine. These beetles tend to last a year, as do the wharf borers, who make round holes and produce a shredded, moist frass. Bark beetles leave little frass in their round exit holes and live as little as a couple of months to a year or more. Spider beetles have a short lifespan of only several months; when making their round tunnels they leave a powdery trail.
Several Boring Years
A few species can enjoy up to several years tunneling their way through wood. Deathwatch beetles spend up to three years producing a gritty frass. Flat oak borers have a lifespan of several years, leaving slightly oval tunnels packed with fine dust. The different species of timber worms don't have a confirmed lifespan, but Texas A & M University estimates them to be several years. The only indication they leave of their presence is round tunnels; they're frass-free beetles.
Weevils, snout beetles and other roundheaded borers have varying lifespans that depend on the specific species. However, one type of roundheaded borer -- the old house borer -- can live up to 32 years, though most only make it to 10 years. The powdery dust these beetles leave behind usually forms pellets. Flatheaded borers make a coarse powder in their tunnels; they can take as long as 30 years to transform.