Termite Swarm Season in Ohio: What to Do When You See Swarmers

A swarm in the basement in April is alarming, and it is the moment people sign the first contract put in front of them. You do not need to. OSU Extension's termite fact sheet says termites feed slowly, there is no need to panic, and a few weeks or even months may be needed to decide on treatment. Use that time to get the identification right and compare written prices.

When termites swarm in Columbus

The eastern subterranean termite is the most common termite in Ohio, per OSU Extension. A swarm is the colony's winged males and females leaving to start new colonies, and only mature colonies, typically several thousand termites, produce them. OSU says swarms are set off when temperature and moisture are right, usually on warm days following rain, and in Ohio that means daytime from March to May. OSU adds that swarms can also show up indoors in other months.

Our weather data shows how spring builds in Columbus. The median last spring freeze at John Glenn airport is April 16. Days with a mean temperature of 50F or higher, a common threshold for insect activity, go from about 8 in March to about 20 in April and nearly every day from May on. Columbus averages 216 such days a year, and 2026 had 215 through October 24, against 201 by that date in an average year.

Insect-active days per month in Columbus (daily mean 50°F or warmer)

The swarm itself is short. OSU says it usually lasts less than an hour, and the swarmers drop their wings soon after. Termites are drawn to light, so the only evidence is often a pile of wings on a basement windowsill, in a cobweb or along a sunny wall. Wings indoors count as a warning sign even if you never saw the insects.

More on reading the numbers is on our Columbus pest data page.

Termite swarmers or flying ants

This is the first question to answer, because ants swarm too. OSU and the EPA describe the differences this way:

	Termite swarmer	Flying ant
Antennae	Straight, like a string of beads	Bent at an elbow
Waist	Thick, no pinch	Narrow, pinched
Wings	Two pairs of equal length that break off easily	Front pair longer than the back pair, and they stay on
Body	Black, about 0.4 inch, soft	Harder body

The color line is OSU's description of the Ohio species, eastern subterranean termite swarmers. A clear close-up photo of one insect from the side, with the wings visible, is usually enough to tell which you have. Carpenter ants have their own page: see ant control in Columbus.

What to do the day you see them

1. Save a few. North Carolina State Extension says to collect some of the insects or wings so a pest control service or extension specialist can identify them. Sweep a dozen into a zip-top bag or a jar and keep it.
2. Do not spray them. NC State notes that swarmers do not cause structural damage; worker termites in the colony do that. Swarmers that end up indoors die from lack of moisture. Bug spray on the swarm kills insects that were already doomed and does nothing to the colony underground.
3. Vacuum the rest. Once you have your sample, clean up.
4. Note where they came out: a crack in the basement floor or a gap at the bottom of a door frame. The person who inspects will want to see it.
5. Book an inspection. NC State says protecting the house starts with a thorough inspection. If you already have a termite contract, call that company first.

I would not sign anything the day of the swarm. OSU's fact sheet suggests getting at least three estimates and being cautious of prices far lower or higher than the others.

Mud tubes on foundations and basement walls

Subterranean termites need moisture, so they build shelter tubes of soil to cross open surfaces between the ground and wood. OSU says the tubes are usually 1/4 to 1 inch wide. In a Columbus house, look:

• Up the inside of basement walls, where the wall meets the sill
• Along the mortar joints of an older stone foundation
• On piers and posts in a crawl space
• Where porch steps, a deck ledger or a garage slab meets the house

OSU's test for an active infestation is simple: break or scrape away a section of tube and check back to see whether termites rebuild it. Damaged wood often looks honeycombed along the grain and packed with soil. OSU suggests probing suspect wood with a flat screwdriver, because hollowed wood gives way and sounds hollow when tapped. It also says houses should be inspected for mud tubes once a year.

Older housing gives termites more to work with. About 35% of homes in the city of Columbus were built before 1960, and in Clintonville the share is 59%. OSU's prevention advice targets what older houses tend to have: wood close to the soil and damp foundations.

What treatment looks like

The EPA lists four kinds of approved termite treatment: liquid soil-applied termiticides, termite baits, building materials impregnated with termiticide, and wood treatments. For an existing Columbus house, the choice is usually between the first two.

Liquid soil treatment

OSU describes it as a continuous treated zone in the soil next to and under the foundation. On a finished house that means trenching along the outside of the foundation and drilling through slabs or along basement walls to inject the product. OSU says effective control often takes 150 or more gallons of diluted termiticide per house, depending on size and whether there is a basement. Gaps in the treated zone let termites around it, which is why OSU calls spot treatments of only the visible area risky except in re-treatment.

The newer non-repellent liquids are not avoided by termites, which forage through the treated soil and carry the active ingredient back to nestmates. OSU says control with these usually comes within 3 months.

Bait systems

Bait stations go in the ground around the house, often starting with untreated monitoring wood. Once termites are feeding, the wood is swapped for a slow-acting bait that workers carry back to the colony. OSU says baits work much more slowly than soil treatments, that it can take several months or more before termites find the stations, and that stations usually need monthly inspections except in harsh winter weather. Baits use far less chemical, and OSU notes they can be used where a soil treatment is a problem, such as houses with wells or cisterns or with heating ducts under the slab.

My view: with an active swarm inside, I would lean toward a liquid treatment for faster control, or a combination the company can explain in writing. A bait-only plan is reasonable when soil treatment is a poor fit, as long as you understand it is a slow program built on service visits, and you know what the yearly renewal costs.

What it costs

This Old House (updated June 17, 2026) puts a termite inspection at $75 to $325, termite treatment at $700 to $2,000 in most cases, and bait systems at $400 to $3,000. Those are national figures, not quotes. Our termite inspection and treatment page covers what to ask for in a written proposal, and this checklist helps you compare two of them.

The Ohio license for termite work

In Ohio, anyone applying pesticides to someone else's property for hire needs a commercial applicator license under ORC 921.06, and termite work has its own category, 10b Termite Control. A commercial applicator license is also required to do wood-destroying insect inspections for real estate sales, per OSU Extension's licensing fact sheet. In the Department of Agriculture's public applicator list, 96 commercial applicators with a Franklin County address hold category 10b, as of October 26, 2026. Ask for the applicator's license number and look it up; our guide to verifying an Ohio pest control license shows how.

Making the house less inviting

OSU's prevention advice comes down to taking away moisture and wood that touch the soil:

• Point downspouts and splash blocks away from the foundation, and grade soil so water drains away from the house.
• Keep at least 6 inches between soil and wooden parts like porch steps and door frames.
• Never stack firewood or lumber against the foundation or in a crawl space.
• Go light on wood mulch right next to the foundation, and remove old stumps near the house.

We only refer companies that hold an Ohio Department of Agriculture pesticide business license and send licensed commercial applicators. If you found swarmers or wings, ask for an inspection and a written price before any treatment.