Drywood vs. Subterranean Termites in the Hill Country: How to Tell Them Apart

The key difference comes down to moisture. Subterranean termites must maintain contact with soil or a persistent moisture source to survive. That is why they build mud tubes along your foundation walls — they cannot tolerate drying out while exposed to air. Their soil dependence is also their weakness: an effective soil treatment creates a chemical barrier they cannot cross. It also means they target moisture-compromised wood and exploit access points from the ground up.

Drywood termites (primarily Incisitermes species in Texas) are physiologically adapted to extract all the moisture they need from the wood itself. They do not need soil contact, do not build mud tubes, and can establish colonies inside completely dry, sound wood — including furniture, picture frames, hardwood floors, and attic framing that has never seen a drop of water. This independence from soil is what makes them difficult to treat with conventional subterranean termite methods.

The clearest sign of drywood termite activity is the presence of frass — tiny, six-sided pellets that look like coarse coffee grounds or sawdust with a distinctive hex shape under magnification. Drywood termites expel this frass from kick-out holes in infested wood, and small piles of it below furniture, window sills, attic framing, or hardwood floors are the characteristic diagnostic indicator. Frass color varies from pale cream to dark brown depending on the wood species being consumed.

Drywood termites swarm in fall in Texas, typically after the first rains following a dry summer — a pattern that coincides with the late-September and October weather typical of the Hill Country. Swarmers (winged reproductives) are reddish-brown, roughly 3/8 inch long including wings, and will shed their wings after landing. Finding shed wings near window sills or light fixtures in fall is a common first indication of an active colony.

Subterranean termites are identified by their mud tubes — pencil-width tunnels of soil, saliva, and debris they construct to protect themselves while traveling between soil and food sources. These tubes are most visible on foundation walls, along the inside of pier-and-beam crawl spaces, and on the exterior of concrete block foundations. Breaking a tube open and returning the next day to see if it has been repaired is a reliable indicator of active infestation.

Subterranean termite damage follows the soft spring growth rings in wood and avoids the harder summer rings, producing a layered, honeycomb appearance. The chambers are typically filled with mud and fecal material. In contrast to drywood termite galleries, subterranean galleries are rarely clean or smooth. Formosan subterranean termites — an invasive species expanding its range into Central Texas — produce especially aggressive colonies and a distinctive carton material (hardened frass and soil) rather than mud in their tubes and chambers.

Subterranean termites are treated with soil-applied liquid termiticides or baiting systems. Liquid treatments create a continuous chemical barrier in the soil around and beneath the structure that kills termites on contact or transfer. Bait stations exploit the colony's social behavior — workers collect bait and share it with the queen and reproductives, eventually collapsing the colony. Both methods require accessing the soil around the structure's perimeter, which is why they have no effect on drywood termites living in above-ground wood.

Drywood termites are treated by localized wood treatment (injecting insecticide directly into galleries through the kick-out holes), whole-structure fumigation with sulfuryl fluoride, or heat treatment. Fumigation remains the only method proven to reach all colonies throughout a structure when the infestation is widespread or in inaccessible locations. Localized treatment is appropriate when the infestation is confirmed to a single, accessible area. Neither approach involves soil application.

Subterranean termites are more common in Texas overall and cause greater aggregate economic damage. However, the Hill Country's hot, dry climate and the elevated presence of aged cedar and hardwood structures make drywood termite activity notably more common here than in wetter parts of the state. Historic Hill Country homes with original cedar lumber framing, tongue-and-groove pine flooring, and minimal humidity control in attics are particularly vulnerable to drywood termite establishment.

It is also possible — and not uncommon — to find both species in a single structure. A home with subterranean termite activity in the foundation sill plates and a drywood termite colony in the attic framing requires a combined treatment program. This is one reason a thorough inspection by a licensed professional, rather than a visual self-inspection, is essential before committing to a treatment approach.