Get a Clue


A key piece of evidence when inspecting a structure for wood-infesting beetles is the insect frass left behind, as well as the size and shape of emergence holes.


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Inspections play a key role in properly identifying the insect pest causing a problem in an account, but if you know what you’re looking for you’ll have a leg up on the competition when it comes to identifying wood-infesting pests. One piece of evidence that is particularly helpful and often left behind by the offending pest is frass.

WHAT IS FRASS ANYWAY? A glossary of entomology defines frass as “solid larval insect excrement,” a nicer word for poop. In the pest control business, we seem to use the term frass only in relation to wood-damaging insects and some people think that frass is just the chewed-up wood debris left by these insects. That’s partially true, but it’s actually wood that has passed through the larva’s digestive system. It no longer looks like wood, except in color.

For wood borers, this “processed” wood poop or frass is made up of wood pellets that are so tiny and dry that they feel powdery, floury and sometimes gritty. Some beetles pack their frass tightly into their galleries and little falls out; others have looser frass that easily sifts from adult emergence holes.

WHAT INSECTS PRODUCE FRASS? Like powderpost beetle larvae, subterranean termites feed on wood but they don’t produce frass. In fact, when sawdust-like material is associated with wood damage, it is not caused by subterranean termites because they don’t produce anything that looks like dry wood shavings or wood pellets. Their feces are more liquid and sometimes mixed with soil and saliva for use as construction material. The galleries of drywood termites, however, do contain something similar to frass in the form of hard, oval-shaped, six-sided fecal pellets. Dampwood termites produce similar fecal pellets. Since these pellets are not produced by feeding larvae, technically they are not considered to be frass.

Carpenter ants don’t produce frass either, but the sawdust material (actual bits of excavated wood) that they dump from their nests is sometimes incorrectly referred to as frass. But if you look under magnification, you will see that the dump piles contain bits of wood, dead ants and pieces of other insects, and debris from the nest site such as bits of insulation or dirt. Carpenter ant galleries don’t contain frass either, but are smooth and clean. If the suspect frass turns out to be carpenter ant dump instead, then you proceed with a different kind of inspection to locate carpenter ants. Look directly above the dump pile for slit-like openings in carpenter ant-infested wood.

If the frass is uniformly shaped and meal-like or flour-like, perhaps with tiny pellets mixed in, you are dealing with a wood-boring beetle. With wood-boring beetle frass, there also will be circular or oval emergence holes in the wood (not seen with termites or carpenter ants), or the frass will be discovered packed into galleries when the infested wood is broken open. The frass that we deal with is usually from powderpost beetles.

If the frass is uniformly shaped and meal-like or flour-like, perhaps with tiny pellets mixed in, you are dealing with a wood-boring beetle. The frass that we deal with is usually from powderpost beetles.

CAN YOU ID THE BEETLE BY FRASS? You can often identify the owner of the frass if you have a good magnifier and a sensitive touch. Collect some of the material and look at it under magnification. Rubbing some frass between your fingers may give you a clue. The size and shape of the emergence holes, as well as the type, age and location of the wood can help narrow down which beetle is infesting:

Lyctine (true) powderpost beetle — Fine and floury frass, with the consistency of talcum powder, feels smooth. Frass loose in tunnels, falls easily from emergence holes. Tiny, round emergence holes.

Bostrichid (false) powderpost beetle — Slightly coarser frass, with meal-like consistency, feels somewhat gritty. Frass tightly packed in tunnels, tends to stick together forming small cakes. Small, round emergence holes.

Anobiid powderpost beetle — Powdery frass, containing pellets (especially when feeding in softwoods), feels gritty. Frass loosely packed in tunnels in softwoods, more tightly packed in hardwoods. Small, round emergence holes.

The authors are well-known industry consultants and co-owners of Pinto & Associates.