Small piles of tiny, gritty pellets on a window sill are one of the most common first signs of a drywood termite infestation. These pellets, called frass, are fecal matter that termites push out of their tunnels through tiny holes in the wood surface. If you’re seeing what looks like a little mound of coffee grounds or coarse pepper collecting on your sill, there’s a good chance drywood termites are living inside the wood above or around your window frame.
What Termite Droppings Look Like
Drywood termite pellets are small, roughly 0.5 to 1 millimeter long. Each pellet is an oval-shaped capsule with six concave sides and rounded ends. This hexagonal cross-section is unique to drywood termites and is visible under a magnifying glass or a zoomed-in phone camera. The pellets are hard and dry to the touch, with a gritty, sand-like texture when you rub them between your fingers.
Color depends entirely on the wood the termites are eating. Pellets can range from light tan to dark brown or nearly black. A single pile sometimes contains pellets of slightly different shades if the termites are feeding through layers of wood with varying color. At a glance, a fresh pile looks like someone sprinkled coffee grounds, coarse salt, or black pepper onto your window sill.
Why They Appear on Window Sills
Drywood termites live entirely inside the wood they eat. Unlike subterranean termites, which build mud tubes and nest underground, drywood species colonize dry, above-ground wood, making window frames, door frames, and trim boards prime targets. As a colony feeds and expands its internal galleries, it needs to dispose of waste. Worker termites carve tiny exit holes, sometimes called kick-out holes, through the wood surface. These holes are about 1 to 2 millimeters in diameter with clean, circular edges.
Termites periodically push pellets through these holes, and gravity does the rest. Because window frames sit directly above a flat sill, the pellets collect in a neat little cone-shaped pile below the hole. You may not notice the hole itself, since termites often seal it with a thin layer of frass and reopen it later. But the accumulating pile on the sill is hard to miss. Tapping gently on the wood above a pile can sometimes dislodge more pellets from the kick-out holes, confirming the source.
Termite Frass vs. Carpenter Ant Debris
Carpenter ants are the other major wood-destroying insect that leaves debris on sills, and the two are often confused. The distinction is straightforward once you know what to look for.
- Shape and uniformity: Termite frass consists of pellets that are remarkably uniform in size and shape. Carpenter ant debris is irregular, a coarse mix of wood shavings, sawdust, and grit with no consistent particle shape.
- Contents: Termite pellets are clean. No insect parts, no wood splinters, just identical gritty pellets. Carpenter ant debris almost always contains visible insect fragments: legs, wings, antennae, and body segments mixed into the pile. This single test is the most reliable way to tell the two apart.
- Texture: Termite frass feels like coarse sand between your fingers. Carpenter ant debris feels fibrous and splintery, more like compressed sawdust.
- Moisture: Carpenter ants prefer damp or previously water-damaged wood. If the area around your window has a history of leaks or condensation, carpenter ants become more likely. Drywood termites, as their name suggests, infest dry wood with no moisture needed.
One important note: subterranean termites do not produce these pellets at all. They use their droppings as construction material for their mud tubes. If you’re finding pellets on a window sill, you’re dealing with drywood termites specifically.
How to Tell if the Infestation Is Active
Finding frass doesn’t automatically mean termites are still present. Pellets can sit inside galleries for years, and vibrations from foot traffic, door slams, or construction can shake old pellets loose through existing holes long after a colony has died or been treated. So the pile on your sill could be fresh, or it could be old debris finally working its way out.
The simplest test is to clean up the pellets completely, then check back in a few days. If a new pile appears in the same spot, the colony is actively feeding and pushing out fresh waste. If nothing reappears after a week or two, the frass may be residual. Keep in mind that building vibrations can also dislodge stored pellets, so a small amount of new material doesn’t always confirm active feeding. A persistent, growing pile is the clearest indicator.
You can also look for other signs nearby. Dead winged termites (swarmers) or small, translucent discarded wings on the sill, in light fixtures, or caught in cobwebs near windows are strong evidence of an active or recent colony. Swarmers emerge through the same kick-out holes to mate and start new colonies, often in spring or early fall depending on your region.
What to Do About It
If your sweep-and-check test confirms active frass production, the colony is inside the wood and won’t go away on its own. Drywood termite colonies grow slowly, sometimes taking years to cause structural damage, but they do cause damage over time as they hollow out wood from the inside.
Treatment depends on the scope of the infestation. A single, localized colony in one window frame can sometimes be treated with a spot treatment, where a pest control professional injects a product directly into the gallery system through the kick-out holes or small drilled access points. This works well when the infestation is limited to one area and you can clearly identify where it is.
The challenge is that drywood termites can infest multiple spots in a home at once, and colonies hidden inside walls or attic framing may not produce visible frass in obvious locations. A professional inspection can determine whether you’re dealing with one colony in a window frame or a broader problem. For widespread infestations, whole-structure fumigation (tenting the house) is the standard approach, since it reaches colonies inside walls and other inaccessible areas that spot treatments can’t.
Preventing Reinfestation
Drywood termites enter homes as winged swarmers that squeeze through surprisingly small gaps. Sealing cracks and joints around window frames, applying paint or varnish to exposed wood surfaces, and ensuring screens on windows and vents are intact and tight-fitting all reduce entry points. Pay particular attention to areas where the window frame meets the exterior wall, since gaps in caulking are a common entry route.
Any time you replace or repair a window frame, use treated wood or non-wood materials for components that won’t be visible. Periodic inspections of window sills, door frames, and attic spaces for new frass piles catch colonies early, before they spread. The earlier a drywood termite colony is found, the more likely a localized treatment can resolve it without the cost and disruption of full fumigation.