Formosan subterranean termites were introduced into Charleston in the mid-1950s and are now established along the coast. They swarm in the evening from mid-May into July, drawn to lights, while native subterranean termites swarm in spring afternoons. People moving infested material, especially old railway ties, is the main reason their range has grown.
Key takeaways
- Clemson dates the arrival of Formosan termites in South Carolina to the 1950s and places their introduction in Charleston in the mid-1950s.
- Clemson lists the species as established in 16 counties, including Berkeley, Charleston and Dorchester.
- People moving infested material, especially old railway ties, are the main cause of the species spreading its range.
- Formosan swarms come later in the year and in the evening, while native subterranean termite swarms come in early spring, usually in the afternoon.
- Clemson's sources describe distribution by county and coastal region, not infestation rates or neighborhood counts.
- Timing and time of day help narrow the species, but a technician confirms it on site before choosing a plan.
Where did Formosan termites come from, and when?
Clemson dates the introduction of Formosan termites to South Carolina to the 1950s, and to the mid-1950s in Charleston.
The Formosan subterranean termite, Coptotermes formosanus, is not native to South Carolina. The Clemson Home and Garden Information Center dates its arrival in the state to the 1950s and places its introduction in Charleston in the mid-1950s. Those dates matter because the termite has had roughly seventy years to spread through the Lowcountry, and a species with that much time in one place is a different kind of problem from a newly arrived one.
Clemson now lists it as established in 16 counties across the state, including Berkeley, Charleston and Dorchester, the three counties that North Charleston spans. Its infestations are concentrated along the coast from Charleston south to Beaufort, and it is found in many areas of Charleston County. Those are distribution facts about the region. They are not a measure of how many houses are affected in any one neighborhood.
How do Formosan termites spread?
People are the main cause of the spread, mostly by moving infested material. Old railway ties are the example Clemson gives.
Clemson's guidance is that people are the main cause of the Formosan termite's expanding range. The mechanism is the movement of infested material. Wood that carries a colony, such as old railway ties, can take the species from one place to another, and a colony established in a new spot can grow and eventually swarm. The spread follows where material goes, not only where the termite already lives.
For a homeowner, this means that the wood on a property matters as much as the soil around it. Timber stacked against the house, old ties used in a garden edge and firewood moved from elsewhere are all things a technician looks at during an inspection. Material that came from somewhere else can carry termites with it, so looking at what is stored or piled against the structure is part of checking for them.
How do you tell Formosan from native subterranean termites?
Timing and time of day are the most useful clues. Native subterranean termites swarm in early spring, usually in the afternoon, while Formosan swarms come later and in the evening.
Clemson describes native subterranean termites as swarming in early spring, usually in the afternoon. Formosan swarms come later in the year and in the evening, which is also when they are drawn to lights. A swarm seen at a porch light in June is therefore a different clue from a swarm seen on a warm afternoon in March, and the difference is the most useful thing a homeowner can notice without special tools.
Timing alone is not a diagnosis. Swarmers are winged reproductives, so a swarm tells you that a colony is nearby, but not how large it is or where it is feeding. Keep any wings or insects you find, and write down the date, the time and the place you saw them. A technician can confirm the species on site, and that confirmation decides which plan fits the house.
Why does the mid-May to July window matter?
Clemson HGIC places Formosan swarms from mid-May into July. Other published accounts put the first emergence in late May or early June, so treat the start of the window as approximate.
The main window Clemson gives is mid-May into July, and the evening is when swarmers are most often seen. Swarmers are drawn to lights, which is why a porch light, a lit window or a street lamp near a house is where a homeowner may notice them first. The window is useful for knowing when to look, but it is not a promise that swarms will appear on any particular night.
Other published accounts put the start of emergence a little later, in late May or early June, so the start of the season varies between reports. The calendar is a guide to when to pay attention, not a substitute for a look at the structure in any month. The work that matters is in the wood and under the house, and a swarm that you never see does not mean the wood is clear.
Why does the Lowcountry house matter for Formosan work?
A vented crawl space puts wood close to damp air and to the soil, which is where termites reach framing. A slab house moves the work to the perimeter and the places where pipes and wiring pass through the slab.
A great many houses in the Charleston area sit over vented crawl spaces in very high humidity. Humid outside air enters the space, and the cool surfaces inside an air-conditioned house, such as ducts and joists, can sit below the dew point of that air. Sustained damp feeds wood-decay fungi and draws termites to the sub-floor, so the crawl space is where a Formosan inspection usually concentrates when the house is raised.
Slab houses change the work rather than removing it. There is no sub-floor to walk under, so the attention goes to the slab edge, the penetrations and the perimeter, where termites can reach the structure from the soil. Piers and pilings sit between the two, with framing open underneath. The Formosan termite is the same species in each case, but the place it is found and the way it is reached differ with the foundation.
Are Formosan termites found in every neighborhood?
The sources give county and regional distribution, not neighborhood counts. A county map cannot tell you how a particular street will fare.
Clemson lists Formosan subterranean termites as established in Berkeley, Charleston and Dorchester counties, and notes that they are in many areas of Charleston County. Those are the levels at which the sources publish their figures. The sources available for this guide do not give infestation rates by neighborhood, and no published map of that kind should be used to rank one area above another.
The housing differs from place to place, and so does the work. The older raised houses on the Charleston peninsula and the sea islands have different framing exposure from the newer slab subdivisions around Summerville and in Berkeley County. Those differences change the scope of an inspection. They do not tell you whether a particular house has termites, and only an inspection of that house can show it. The area page for Charleston describes the peninsula housing in more detail.
What should a homeowner do after seeing a swarm?
Keep the evidence, note when and where it happened, and ask for an inspection of the structure. A single swarm is a reason to look, not a reason to assume the worst.
A swarm at a light in the evening is a reason to look carefully, not a reason to panic. Note the date, the time and where you saw the insects. If you can, keep a few of the wings or insects in a sealed container, because a clear sample helps the technician confirm the species on site. A photograph taken from a short distance also helps when the insects are no longer in the house.
When you ask for a visit, say that you saw swarmers and when. Phones are answered 24/7 at (855) 974-4733, and a visit the same day is possible only when a technician is free. Ask for an inspection that covers the structure, the crawl space or slab and the material around the house, because the swarm itself tells only part of the story.
How do Formosan termites fit into the wider termite picture?
Formosan termites are one of several termites in the Lowcountry. Native subterranean termites and drywood termites are separate problems, with separate plans.
Formosan termites add a dimension to termite work in the Lowcountry because of their established range, their evening swarms and their spread by people. They do not replace the native subterranean termites, which swarm earlier in the year and in the afternoon. A proper inspection looks for which termites are present, not just whether termites are present at all, because the answer changes the plan.
Drywood termites are a separate category. They nest inside the timber itself with no soil contact, so a soil barrier does not reach them. That is why an inspection names the species and the place of the damage rather than treating termites as one problem. A plan that is right for a subterranean colony in the soil may be the wrong plan for a drywood colony in a beam or a sill.
Frequently asked questions
Are Formosan termites the same as native subterranean termites?
They are both subterranean termites, so both depend on soil contact and moisture. They are not the same species. Clemson separates them partly by swarm timing: native swarms come in early spring, usually in the afternoon, while Formosan swarms come later and in the evening. A technician confirms the species on site before choosing a plan.
How did Formosan termites get to Charleston?
Clemson says the species was introduced to South Carolina in the 1950s, with the mid-1950s date given for Charleston. People are the main cause of its spread, particularly by moving infested material such as old railway ties. The species has been established in Charleston for decades, and Clemson lists it in 16 counties. The sources used here do not describe a single route into the state.
When do Formosan termites swarm?
The main window Clemson gives runs from mid-May into July. Swarms are most often seen in the evening, when the insects are drawn to lights. Other published accounts put the start of emergence in late May or early June. Treat the start of the season as approximate and look at the house in any month.
Why do Formosan swarms gather at my porch light?
Formosan swarmers are drawn to lights in the evening, which is why a porch light, a lit window or a street lamp is where they are often seen. A swarm at a light shows that a colony is nearby, but it does not say how large the colony is or where it is feeding. Note the date and the time, and report what you saw when you ask for an inspection.
Can a homeowner tell Formosan termites apart by sight?
The sources used here do not describe a dependable identification by eye. The clues Clemson gives are timing and time of day, along with the look of the swarm itself. Collect a few wings or insects if you can, and let a technician confirm the species on site. A confident guess from a photograph is less useful than a sample checked in person.
Does a swarm mean my house is damaged?
A swarm does not by itself show that there is damage, and the absence of a swarm does not show that there is none. Damage is found by inspecting the structure, especially the wood under the house and at the perimeter. Ask for a look at the structure rather than relying on what you have seen flying around a light.
Sources
This guide is general information for Charleston homeowners, not a substitute for an on-site inspection. Prices are estimates. See our disclaimer.