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Frass, pellets, and powder

Rub a little of the material between finger and thumb. Texture separates three very different wood pests, and this single test is more informative than anything you can see from across the room.

How to examine it

  1. Collect a sample onto white paper, which makes colour and particle size visible in a way a dark floor does not.
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  3. Look at individual particles under a hand lens. Six-sided pellets with concave faces are unmistakable once seen.
  4. Note the wood it came from. Large-pored hardwood — oak, ash, hickory, walnut, bamboo — versus softwood framing narrows it immediately.
  5. Look for the hole above the pile. Round and 1–2 mm, or a small irregular kick-out hole, are different insects.
  6. Clear the pile completely, mark the date, and check again in two weeks. Fresh material means active; nothing means the damage is historical.
What each species leaves, and how to tell them apart
SpeciesHow to tell
Drywood termiteHard, gritty, six-sided pellets about 1 mm with concave faces, like coarse sand. Colour varies and does not indicate the wood colour.
Powderpost beetleExtremely fine talc-like powder that flows freely like flour. Only in large-pored hardwood — oak, ash, hickory, walnut, bamboo.
Carpenter antCoarse fibrous shavings, not pelletized and not powdery, usually with insect body parts mixed in.
Subterranean termite mud tube compared with drywood termite frass pelletsTwo kinds of termite evidence. On the left, a subterranean termite mud tube: a pencil-width column of packed soil running up a foundation wall from the ground. On the right, drywood termite frass: hard pellets about one millimetre long, six-sided in cross-section with concave faces, which collect in small piles beneath tiny kick-out holes. Mud tubes mean subterranean termites; pellets with no mud tubes mean drywood termites.Subterranean: mud tubepencil-width, soil, on foundationDrywood: frass pellets1 mm, hard, six-sided

Compared at scale. The features are described in words in the table above.

What else gets mistaken for this

  • Sawdust from a past repair, alteration, or drilling, which is coarser and more varied in particle size than any insect frass, and does not reappear once cleared.
  • Drywall and plaster dust, which is chalky white or grey and smears rather than flowing.
  • Pollen, which is seasonal, appears on horizontal surfaces throughout a room rather than beneath a hole, and is uniformly fine and yellow.
  • Decayed wood crumbling from wet rot, which produces a soft brown powder but no exit holes and no gallery structure.
  • Dust and lint accumulating on a windowsill, which is the surface where drywood pellets also collect and where the two are most often confused.

What this evidence cannot tell you

Texture identifies the insect group reliably. It says nothing about how much timber is affected, and nothing about how long the infestation has been running — a small pile can come from a long-established gallery system, and a large pile from a single active member. It also cannot confirm the infestation is current on its own. Frass sits where it falls for years, which is why the clear-and-recheck test matters more than the quantity in front of you.

What to do with what you found

Hard six-sided pellets mean drywood termites, and the question that follows is extent — how many members are infested — because that decides whether a localised approach is viable or whole-structure work is being proposed. Flour-fine powder means powderpost beetles, and it comes with a structural reassurance worth having: they attack only large-pored hardwood, so softwood framing is not at risk from them. Confirm the wood is hardwood before accepting a quote written for something larger. Coarse fibrous shavings with insect parts mixed in are not frass at all — they are carpenter ant excavation debris, and the moisture that made the timber habitable is what to look for.

Common mistakes

  • Judging by colour rather than texture. Frass colour varies and does not indicate the wood or the species.
  • Sweeping the pile away before photographing and dating it, which discards the activity test.
  • Accepting whole-structure work without an extent finding that justifies it in writing.
  • Assuming powderpost beetles threaten structural framing. They do not — only large-pored hardwood is at risk.
  • Confusing carpenter ant shavings with frass, which sends the response to the wrong insect and away from the moisture problem.

Not sure?

Your county extension service will often identify a specimen at no cost, and that is more useful than a confident guess.

Start the identification key

Sources

Every claim on this page traces to one of these.

  1. Cooperative Extension System Tier 2. University extension entomology resources.
  2. University of California Statewide IPM Program Tier 2. UC IPM Pest Notes.
Reviewed by AgainstPest Editorial Team Last reviewed: