What Are the Warning Signs of a Summer Termite Swarm?
A summer termite swarm is most often indicated by the sudden appearance of winged reproductive termites (alates) near lights or windows, discarded translucent wings clustered on sills or floors, and swarms of tiny, ant‑like insects emerging from wood, crawlspaces, or soil vents. Other common warning signs include mud tubes or soil-packed galleries along foundations (typical of subterranean termites), small piles of pelletized frass beneath infested wood (common with dampwood or drywood species), soft or hollow-sounding structural members, and swarming activity shortly after warm, calm evenings or rain.
This issue is especially relevant for Pacific Northwest homeowners because the region’s mild, wet climate and abundant coniferous timber create ideal conditions for local termite species—most notably dampwood termites (e.g., Zootermopsis spp.) and subterranean Reticulitermes species—to establish and reproduce. The prevalence of older homes, exposed wood siding and decking, and frequent moisture retention in basements, crawlspaces, and landscaped stumps increases the likelihood of concealed infestations; many PNW termite species exploit persistently damp wood, so visible swarm indicators such as discarded wings and frass are often the first outward signs of a deeper, hidden problem.
Which termite species swarm in Seattle and the Pacific Northwest during summer
Two species dominate summer swarms in the Seattle area: the western subterranean termite (Reticulitermes hesperus) and the Pacific dampwood termite (Zootermopsis angusticollis). R. hesperus is the common subterranean species across Puget Sound lowlands and nests in soil or wood in direct contact with soil. Zootermopsis is native to western Washington and establishes colonies in naturally damp, decayed wood above ground—stumps, log piles, and high‑moisture structural members are typical sites.
Their seasonal timing differs in predictable ways. R. hesperus most often produces winged reproductives in late spring into early summer (commonly April through June in metro Seattle), with flights concentrated on warm, calm evenings soon after sunset. Pacific dampwood termites tend to swarm later, peaking in mid to late summer—July and August—and can extend into September during warm, humid stretches; dampwood flights often follow several days of daytime highs above roughly 70°F (≈21°C) or after warm, humid nights.
Colony scale and the type of structural risk also separate them. Mature subterranean colonies in the PNW commonly number in the tens of thousands to a few hundred thousand individuals (many field estimates cite 50,000–300,000 for established R. hesperus colonies), and they cause diffuse structural damage by tunneling and maintaining mud tubes to reach multiple wood sources. Dampwood colonies are typically localized to single wet timbers and, while individual colonies are usually smaller—often in the low thousands to tens of thousands in a saturated log—they can cause severe, localized decay because dampwood feeds in wood with moisture contents usually above ~20%.
Other termite types are rarely involved in Seattle summer swarms. True drywood termites (Incisitermes species) are common farther south in California but are seldom established in western Washington; most reports in this region are associated with driftwood or imported timbers rather than local colonies. Local factors matter: dampwood is most frequent in the low‑elevation, high‑humidity coastal and urban forest fringe around the Sound, whereas subterranean infestations correlate with soil contact, standing landscape moisture, and features such as mulch deeper than ~3 inches placed within a foot of a foundation.
What do swarming termites and their discarded wings look like in Seattle homes
Swarming reproductives in the Pacific Northwest fall into two visually distinct groups: dampwood alates (Zootermopsis angusticollis) and smaller subterranean alates (Reticulitermes spp.). Dampwood swarmers are noticeably larger, with body lengths commonly in the 10–15 mm range and paired wings that extend to 25–30 mm, producing an overall insect length approaching 1 inch when wings are included. Subterranean alates are slimmer and darker, with body lengths typically 5–8 mm and wings roughly 8–12 mm long. Dampwood alates are usually light tan to reddish-brown; subterranean alates are medium to dark brown or black. Both have two pairs of equal-sized, translucent wings with multiple fine veins; unlike ants, the forewings and hindwings match in size and shape.
Discarded wings in Seattle homes present as thin, translucent sheaths that catch easily in window tracks, on sills and under light fixtures; individual wings measure from about 8 mm (subterranean) to 30 mm (dampwood). Homeowners often find wings in symmetrical pairs or small clusters of 10–100 pieces concentrated where alates landed and shed. The wings are papery and glossy, usually intact rather than shredded; their trailing edges are smooth and may show a faint smoky tint. Because wings are buoyant to drafts, they commonly accumulate in linear piles along the inside edge of blinds, in the crevice between the window and frame, or in the corners of exterior eaves and porch railings.
In Seattle’s moist coastal climate, dampwood alates are the most likely source of larger wing piles found on or under wooden exterior elements—soffits, decks and rotten fascia—because dampwood colonies develop in wood with sustained moisture content above roughly 20–25%. Subterranean alates, which require soil contact for colonies, tend to enter through small gaps around doors and windows and leave smaller, darker wings inside upper-story windows or near light fixtures. After a warm, humid evening swarm, it is common to find a concentration of wings the next morning directly beneath the light source that attracted them, giving a clear indicator of their entry point and flight path.
The condition and location of wings also give diagnostic cues: intact, glossy wings in neat piles on exterior wood or under eaves usually point to nearby dampwood activity in saturated or decayed timber, whereas scattered, smaller wings inside a room—often mixed with dead alates—are more typical of subterranean swarms that flew in through gaps. Quantitatively, a single small subterranean swarm might leave 20–50 wings visible indoors, while a dampwood emergence from a localized log or rotten sill can deposit 50–200 wings on adjacent surfaces. Observing the size, color and exact accumulation spot of wings provides reliable, measurable evidence for distinguishing the two swarm types in the Seattle area.
How can you distinguish termite swarmers from carpenter ants in the PNW
Begin with body shape and antennae: PNW termite alates (both Western subterranean Reticulitermes hesperus and Pacific dampwood Zootermopsis angusticollis) have a nearly uniform, cylindrical body without a constricted waist and straight, bead‑like antennae 10–20 segmented. Subterranean alate bodies typically measure about 4–8 mm long (0.16–0.31 in), dampwood alates run larger at roughly 9–12 mm (0.35–0.47 in). Carpenter ant alates (Camponotus spp.) display a visibly pinched waist with one or two petiole nodes creating a 0.5–1.5 mm constriction and distinctly elbowed (geniculate) antennae; their body lengths generally fall between 6–13 mm (0.24–0.51 in). Those three features — uninterrupted waist, straight vs. elbowed antennae, and relative body size — are the quickest morphological checks indoors.
Wing characteristics provide a second, measurable clue. Termite alates have two pairs of wings of equal length that commonly exceed the body length by 1.5–2×: subterranean alate wings are often 10–15 mm long, dampwood wings can reach 20–25 mm. Carpenter ant alates have unequal front and hind wings, with the forewings typically 20–30% longer than the hind wings; overall wing veins on ants are fewer and thicker compared with the more numerous, parallel veins in termite wings. After flights, subterranean and dampwood termites commonly shed both pairs of wings intact, producing piles of nearly identical translucent wings 8–25 mm long near window sills or exterior lights; ant wing piles will show two distinct sizes corresponding to fore and hind wings.
Flight behavior and timing in the Seattle region also help separate the two. Reticulitermes subterranean swarms in the PNW most often occur from late spring into early summer (April–July) during warm, humid conditions—air temperatures above roughly 13–16°C (55–60°F) with recent rain or high overnight humidity—and are typically seen as sluggish, short flights toward light sources during mid‑morning. Dampwood termites tend to swarm later in summer and may be attracted to porch or indoor lights at dusk or night. Carpenter ant nuptial flights in western Washington generally peak at dusk between June and August on warm, wind‑calm evenings; their alates fly higher and more directly and can disperse farther from the nest than termite alates.
When you inspect a pile of discarded wings or live alates inside a Seattle home, cross‑check three measurable points: antenna shape (straight/beaded vs. elbowed), waist profile (broad vs. constricted petiole(s)), and wing equality/length (equal and 1.5–2× body length vs. unequal fore/hind wings). Correlate those observations with the season and recent weather—mid‑morning swarms after warm, rainy nights point toward subterranean termites, dusk flights in high summer favor carpenter ants, and very large, slow alates with wings up to 25 mm in length suggest dampwood termites.
What structural or environmental signs indicate a dampwood termite infestation in Pacific Northwest homes
Dampwood infestations in the PNW are strongly tied to sustained wood moisture: Pacific dampwood termites (Zootermopsis spp.) colonize wood with moisture contents typically above 20% and become far more likely when readings reach 25–30% or higher on a pin or pinless moisture meter. In Seattle-area houses this most often occurs in roof eaves and wall cavities with chronic leaks, in attic framing where a flashing failure allows seasonal wetting, and in crawlspaces with slow plumbing leaks. Because dampwood colonies prefer already-decayed or fungus‑attacked timber, visible fungal staining or soft, decayed patches (where wood fibers separate easily) within 6–12 months of a persistent leak are a common precursor to active infestation.
Structural signs differ from those left by subterranean termites: dampwood galleries are usually roomy and smooth‑walled rather than narrow mud tubes, and you can often probe into them directly. A practical field sign is wood that yields to a screwdriver tip under light hand pressure by more than 6 mm (about 1/4 inch) over an area larger than a coin — especially where paint blisters or the surface buckles over a span of several inches. Galleries and chambers visible after removing a small section of siding or soffit are commonly 1–3 cm in diameter and may be filled with wet, fibrous frass and shredded wood rather than the hard, six‑sided pellets produced by drywood species.
Environmental indicators around the building are specific and measurable: repeated ponding within 0.5–1.0 m (1.5–3 ft) of exterior walls, downspouts that discharge against foundation walls, or wood‑to‑soil contact such as stacked firewood and tree stumps within 1–2 m (3–6 ft) of the house substantially raise the likelihood of a dampwood source colony. Indoor microclimates matter — crawlspace relative humidity consistently above 60% and attic areas where moisture readings exceed 20% during the summer months correlate strongly with dampwood activity in Seattle’s maritime climate. Because Pacific dampwoods are linked to rot, visible white or brown soft-rot pockets behind siding or under deck boards are reliable environmental red flags.
Signs tied to colony activity and spread are also distinctive: dampwood alates (swarmers) in the PNW tend to fly only short distances, so finding large, intact winged termites or piles of discarded wings concentrated directly under eaves, around attic vents, or on window sills is a spatial clue pointing back to nearby infested wood. Unlike drywood infestations that leave small hard pellets scattered beneath walls, dampwood infestations often retain frass within galleries or produce wet, granular piles at exit holes; discovering moist frass and live nymphs when a suspected member of framing is opened indicates an active colony. If moisture conditions remain unchanged, structural degradation can progress visibly — loss of cross‑section in joists or rafters exceeding 25% can develop over 2–5 years in continuously wet wood, whereas transient wetting typically produces slower, less extensive damage.
When during summer are PNW termite swarms most likely and which weather conditions trigger them
In the Seattle/Puget Sound region, the summer swarming picture is dominated by dampwood termites (Zootermopsis spp.), whose alate activity is most likely from July through September; warm-season peaks often shift a few weeks later in cooler years. Western subterranean termites (Reticulitermes hesperus) produce most of their flights earlier in the year — typically late spring into early summer (May–June) — so true mid‑ to late‑summer swarm reports around Seattle are usually dampwood origin rather than subterranean. Average July highs in Seattle (~73–76°F / 23–24°C) align with the dampwood window, whereas subterranean flights correlate with spring warming when daytime highs first consistently exceed ~60–65°F (15–18°C).
Specific short‑term weather conditions trigger most swarms. Empirical observations in the PNW show alates emerge when ambient temperatures are in roughly the 65–80°F (18–27°C) range and relative humidity is high (commonly >70%). Subterranean Reticulitermes swarms most often occur within 24–48 hours after a warm rain that raises soil moisture; a single warm shower of 0.1–0.5 in (2.5–12 mm) can be sufficient to initiate flights if temperature thresholds are met. Dampwood swarms are more closely tied to elevated wood moisture (see next paragraph) and to humid, overcast or foggy evenings that follow several days of warm weather rather than a single spring storm.
Daily timing and flight dynamics differ by species and are weather‑sensitive. Reticulitermes alates usually fly at dusk into the early evening and their flights commonly last 15–90 minutes after emergence; they tend to fly short distances, typically under 50–100 meters from the natal nest. Dampwood alates in the PNW will often take off in late afternoon through night on warm, humid days and can also fly during daylight if skies are overcast; flights likewise are brief, and discarded wings cluster near exterior lighting, windows, and soffits within a few meters of the emergence point. Wing shedding typically occurs within minutes to a couple of hours after landing, so finding intact piles of translucent wings concentrated under eaves or window sills is a temporal indicator of a recent swarm.
Local microclimates around Seattle influence summer swarm likelihood despite the region’s generally dry July–August pattern. Irrigated lawns, leaky gutters, and south‑ or west‑facing decks create pockets where wood and soil moisture stay elevated; dampwood colonies establish in wood with moisture content generally above ~20–25% and will produce alates reliably when those local moisture conditions coincide with warm nights. Coastal stretches and lowland riparian corridors that retain fog or higher humidity can extend the swarming window into September or October, whereas dryer urban cores without persistent moisture see a narrower mid‑summer swarm season concentrated in the warmest, most humid episodes.
What do discarded termite wings look like and where will I find them in my Seattle home?
Termite wings are thin, translucent, glossy and usually shed intact in matching pairs; sizes range from about 8 mm (subterranean) up to 25–30 mm (dampwood). They commonly accumulate in window tracks and sills, under light fixtures, in the crevices of blinds, and on or under exterior eaves, soffits, decks and porch railings near the emergence point.
How can I tell if the wings I found are from termites or carpenter ants?
Check body and antenna features: termites have a broad, unsegmented waist and straight, bead‑like antennae, while carpenter ant alates have a constricted waist and elbowed antennae; termite wings are equal in size, ants’ fore- and hind‑wings differ. After flights, termites typically drop two equal pairs of intact wings (many matching pieces), whereas ant wing piles show two different wing sizes corresponding to fore and hind wings.
What structural signs indicate a dampwood termite infestation in Pacific Northwest homes?
Dampwood infestations are tied to sustained wood moisture (typically >20–25% on a moisture meter) and show soft, decayed wood that yields to a screwdriver or fingers, roomy smooth galleries, and wet or fibrous frass often retained in galleries or at exit holes. Look for infestations in chronically wet areas such as rotten fascia, soffits, attic framing with flashing leaks, nearby stumps or stacked wet firewood, plus crawlspaces with relative humidity consistently above ~60%.
When are termite swarms most likely in Seattle and what weather triggers them?
In the Seattle/Puget Sound area, subterranean Reticulitermes swarms peak in late spring to early summer (May–June) while dampwood Zootermopsis swarms peak mid to late summer (July–September). Flights are triggered by warm, humid conditions (roughly 65–80°F / 18–27°C and relative humidity commonly >70%); subterranean swarms often follow warm rain within 24–48 hours, whereas dampwood swarms correlate with sustained elevated wood moisture and warm humid nights.