Signs of Termite Infestation

Termite infestations cause an estimated $5 billion in property damage annually in the United States (U.S. Department of Agriculture Forest Service), yet the insects responsible are rarely visible until structural damage is already underway. Recognizing the physical evidence termites leave behind — from mud tubes to hollow wood — is the first step in determining whether professional assessment is warranted. This page covers the major observable signs of termite activity, how each sign is produced, the species most commonly linked to each indicator, and the thresholds that separate casual monitoring from urgent action.

Definition and scope

A "sign of termite infestation" is any physical evidence that termites are or have been active in a structure or on a property. These signs divide into two categories: active infestation indicators (evidence of live colonies currently foraging or tunneling) and historical damage indicators (structural evidence that feeding occurred, with no guarantee of ongoing activity).

The distinction matters because termite damage assessment and treatment decisions depend on whether a colony is still present. The U.S. Environmental Protection Agency classifies termites as wood-destroying organisms (WDOs) under its pesticide regulation framework (EPA Pesticide Registration), and all 50 states require licensed pest management professionals to perform WDO inspections under their own pest control licensing statutes — see termite control licensing requirements for state-level detail.

The three termite groups most relevant to U.S. property owners are subterranean, drywood, and dampwood termites. Each produces a distinct set of signs, described in the sections below. Termite species identification covers full taxonomic breakdowns; this page focuses specifically on what property owners and inspectors observe.

How it works

Termites produce visible evidence as a byproduct of their biology and behavior. Understanding the mechanism behind each sign helps distinguish termite activity from superficially similar damage caused by carpenter ants, wood-boring beetles, or moisture decay.

Mud tubes

Subterranean termites (Reticulitermes, Coptotermes, Nasutitermes, and related genera) cannot survive exposure to open air — their cuticle desiccates rapidly. To travel between their underground colony and above-ground food sources, workers construct sealed earthen tunnels called mud tubes, built from soil, fecal material, and saliva. Tubes typically measure 6–12 mm in diameter. They appear on foundation walls, pier blocks, floor joists, and any surface connecting soil to wood. Full identification guidance is available at termite mud tubes identification.

Frass (fecal pellets)

Drywood termites excavate galleries entirely within wood and push fecal pellets — called frass — out through small kick-out holes. Frass pellets are roughly 1 mm in length, hexagonal in cross-section, and range in color from tan to dark brown depending on the wood being consumed. Accumulation of 30–100 pellets beneath a kick-out hole is the most reliable visual sign of active drywood activity. Detailed morphology is covered at termite frass identification.

Swarmers (alates)

Reproductive termites with wings — called alates or swarmers — emerge from mature colonies in large numbers to establish new colonies. Indoor swarming, or the discovery of discarded wings near windowsills, door frames, or light fixtures, is a strong indicator of an established colony within or immediately adjacent to the structure. Termite swarmers vs. flying ants covers the morphological differences in detail. Subterranean species typically swarm in spring; drywood species often swarm in late summer or fall, tied to local temperature thresholds (University of Florida IFAS Extension).

Hollow or damaged wood

Termites consume wood from the interior outward, leaving a thin outer shell intact. Tapping suspect structural members with a screwdriver handle produces a papery or hollow resonance. Probing with the screwdriver tip may reveal galleries running parallel to the wood grain in subterranean species, or a honeycombed, cross-grain pattern in drywood species.

Moisture and surface blistering

Formosan subterranean termites (Coptotermes formosanus) sometimes construct carton nests — secondary nests of chewed wood, soil, and secretions — within wall voids. These nests retain moisture and can cause paint to blister or bubble, mimicking water damage. Formosan termite control addresses the specific challenges of this invasive species.

Common scenarios

The following structured breakdown covers the five most frequently encountered sign combinations in residential and light-commercial inspections:

1. Mud tubes on exterior foundation wall, no visible wood damage — Indicates active subterranean foraging along the path toward interior wood members; colony may not yet have caused significant structural damage.
2. Frass piles beneath wooden furniture, trim, or window frames — Classic drywood sign; galleries may be confined to a single piece of furniture or extend into structural framing behind wall surfaces.
3. Swarmer wings accumulated on interior windowsills in spring — Subterranean colony is mature (typically 3–5 years old) and has produced reproductives; the colony itself may be entirely below grade.
4. Hollow sound in floor joists or subfloor decking with no mud tubes — Possible historical subterranean damage or active drywood infestation in crawl space framing; requires probe inspection to differentiate.
5. Paint blistering on interior wall near plumbing or HVAC penetrations — Formosan carton nest possibility; moisture meter readings above 19% in adjacent wood members support further investigation.

Termite season and activity patterns and termite risk by U.S. region provide geographic and seasonal context for interpreting these scenarios.

Decision boundaries

Not every sign demands the same urgency or response. The table below maps sign type to severity framing consistent with termite infestation severity levels:

Subterranean vs. drywood comparison: Subterranean signs (mud tubes, spring swarmers, hollow grain-parallel galleries) are tied to soil contact and moisture movement; drywood signs (frass pellets, late-season swarmers, cross-grain galleries, no soil contact) are fully aerial and require different treatment modalities. Conflating the two leads to incorrect treatment selection — termite treatment methods comparison covers the treatment logic in detail.

Signs observed during a real estate transaction carry specific legal weight under wood-destroying organism report requirements in most states. Wood-destroying organism reports explained and real estate termite inspection requirements cover the disclosure and inspection obligations that apply.

Professional pest management inspectors operating under National Pest Management Association (NPMA) standards and state-issued licenses use the sign categories above as the basis for WDO report completion. The NPMA's pest management standards and the International Residential Code (IRC) Section R318 both recognize termite evidence classification as a prerequisite for treatment specification (International Code Council).

References

• U.S. Environmental Protection Agency — Termites: How to Identify and Control Them
• USDA Forest Service — Wood Handbook, Chapter 14: Wood Preservation
• University of Florida IFAS Extension — Subterranean Termites (EDIS)
• National Pest Management Association (NPMA) — Pest Management Standards
• International Code Council — International Residential Code, Section R318 (Protection Against Decay and Termites)
• EPA Pesticide Registration — Wood-Destroying Organisms