Termite Season in Delaware County: What Spring Swarms Mean

When do termites swarm in Pennsylvania?

Eastern subterranean termites, the species behind nearly all termite damage in this region, usually swarm from about March through May. The trigger is a warm, still day, often right after rain, when soil moisture and temperature line up. Swarms typically happen in daylight and last less than an hour.

A swarm is how a colony reproduces. Winged males and females leave the nest, pair up, drop their wings and try to start new colonies in moist soil or wood. Most of them fail, but the colony they came from is still there, still feeding.

Termite swarm in spring: inside vs outside

Where you see the swarm matters. Swarmers outside, around a stump, a fence post or a woodpile in the yard, show that termites are active on your property. That is worth an inspection but not cause for alarm.

Swarmers inside the house are a different story. They almost always emerged from a colony feeding in or under the structure, often through a crack in a slab, around a basement window, near a bathtub drain or at a door frame. Indoor swarmers cannot survive long; they head toward light and die within hours. The colony that produced them remains.

How old is a colony that swarms?

Older than most people expect. An Eastern subterranean termite colony usually needs several years of steady growth before it produces winged swarmers at all, so a swarm in April means termites have been feeding nearby for a while. A mature colony can hold tens of thousands of workers or more, spread through a network of underground galleries.

Those workers forage well beyond the nest, often across a large part of a suburban lot, following roots, buried wood and moist soil. That is why the source of a swarm in the basement may sit under the slab porch, a buried form board or a dead tree by the driveway rather than directly under the spot where the swarmers came out.

Is it a termite or a flying ant?

Carpenter ants and other ants swarm in spring too, and the two get confused constantly. These features tell them apart:

What to do in the first day after a swarm

1. 1

   Do not panic or tear into walls

   Termite damage builds over years. A few days to schedule an inspection will not change the outcome.

2. 2

   Save samples

   Collect several swarmers and some shed wings in a sealed bag or jar. A clear sample makes identification quick.

3. 3

   Take photos and note the location

   Record exactly where they came from: a window, a crack in the floor, a baseboard, a door frame.

4. 4

   Vacuum the rest

   Spraying swarmers does nothing to the colony and can make the source harder to find.

5. 5

   Schedule an inspection

   Have the foundation, basement, crawl space and any wood near soil checked for mud tubes and damage.

Subterranean termites in Delaware County homes

Southeastern Pennsylvania lies in a moderate-to-heavy subterranean termite zone, and Delaware County's housing stock gives termites plenty of opportunities. Many neighborhoods were built after World War II, and Census (ACS) estimates put the median home build year in Springfield Township at 1955. Cape Cods and colonials from that era often have slab porches, attached garages, basement windows set low to the ground and wooden sills sitting close to soil.

Termites build pencil-width mud tubes to travel from the soil to wood without drying out. Look for them on foundation walls, piers, sill plates and the backs of basement stairs. Mulch piled against siding, firewood stored against the house, leaky gutters and wood siding that touches the ground all make it easier for termites to reach the structure unseen.

A spring walk-around that makes the house less inviting

Swarm season is also a good weekend to take away the conditions termites use to reach wood unseen. Walk the outside of the foundation with a flashlight and work through this list:

• Rake mulch back a few inches from the foundation and keep the layer thin, so you can see the wall where it meets the soil.
• Make sure downspouts discharge several feet from the house and that soil slopes away from the foundation.
• Pull firewood, lumber scraps and old fence posts away from the walls and up off the ground.
• Look for wood siding, trim, door frames or deck posts touching soil, and note any spot with less than about six inches of clearance.
• Check the crawl space or basement for standing water, sweating pipes and damp sills, and run a dehumidifier where the air stays wet.
• Remove old stumps and buried wood near the house where you can; they feed colonies close to the structure.

Should you get a termite inspection in spring if you saw nothing?

It is a reasonable time to do it. Spring is when colonies are most active near the surface, so mud tubes and fresh damage are easier to find, and many homeowners schedule a termite inspection around swarm season for exactly that reason. Homes with a past treatment, a finished basement that hides walls, or a history of moisture problems benefit most.

If an inspection does find activity, treatment options include liquid soil treatments and in-ground bait stations, each with trade-offs that our termite control page explains. If the insects turn out to be ants, our carpenter ant control page covers the other common wood-damaging pest in this area.