St. Louis Pest Control Calendar: What Shows Up Every Month

Pest pressure in St. Louis isn't random. It runs on a schedule, and once you know the schedule you stop being surprised by it.

This is the calendar we work off. It's built from what we actually find on service calls across St. Louis County, St. Charles County and Jefferson County, not from a national template.

The short version

Ants and spiders are your spring and summer problem. Mosquitoes and ticks own the middle of the year. Rodents are a fall and winter problem that starts earlier than most people think. Brown recluse never really leave, they just get more visible when it warms up.

January

Quiet month outside, busy month inside. Mice that moved in during the fall are established now and breeding in wall voids and attics. This is when people finally hear the scratching, because the house is quiet and everyone's home.

Spiders are still active in basements and crawl spaces, feeding on whatever overwintered with them.

What to do: if you're hearing anything overhead or in the walls, deal with it now. A January mouse problem is a March mouse infestation.

February

Same as January, plus the first warm stretch. St. Louis usually gets a few 60-degree days in late February, and every one of them wakes something up. Cluster flies and box elder bugs come out of window frames and attic corners, which confuses people who thought winter had handled it.

They didn't hatch. They were sleeping in your walls the whole time.

March

Overwintering ants get moving. Odorous house ants and pavement ants start foraging, usually along the same interior trails they used last year.

Termite swarm season starts late in the month if it's warm. Swarmers look like flying ants and come out of the ground near foundations, usually on the first warm humid day after rain.

What to do: March is the single best month to start quarterly service. You're getting a barrier down before pressure builds, not chasing something that's already inside.

April

Everything wakes up at once. Ants go hard. Wasps start building. The first mosquitoes appear as soon as we get standing water and consistent 50-degree nights.

Ticks become a real concern in wooded parts of Wildwood, Eureka, Chesterfield and anywhere backing to a tree line.

What to do: mosquito and tick treatments start in early-to-mid April here. Starting in June means you spent May getting bitten for no reason.

May

Peak ant month. If you're going to have an ant problem, May is when it announces itself in the kitchen.

Carpenter ants get active around moisture-damaged wood: deck ledger boards, window frames, anywhere a gutter has been overflowing. Bigger, slower, black, and a sign of a moisture problem as much as a pest problem.

Brown recluse become noticeably more visible as temperatures rise.

June

Mosquito season hits full stride. Wasp and hornet nests become obvious under eaves, in soffits and in grill covers.

Yellowjackets are still small colonies in June, which is exactly why June is the easy month to deal with them. In August they aren't easy.

July

Hot and dry pushes pests toward moisture, which means toward your house. Ants show up in bathrooms and around dishwashers. Spiders move into garages.

Mosquito pressure peaks after every storm. Anything holding water for a week becomes a nursery: clogged gutters, saucers under planters, a tarp with a dip in it, a forgotten kid's pool.

August

Peak wasp aggression. Colonies are at maximum size and the workers get bold around food and drinks. This is the month people get stung at their own barbecue.

Late August is when the first rodent scouts start testing foundations. It feels early. It isn't.

September

Rodent season starts for real. The first cool nights send mice looking for somewhere warm, and a mouse fits through a gap the width of a pencil.

Spiders become more visible indoors as they follow their food inside. Stink bugs and Asian lady beetles start massing on warm south-facing walls.

What to do: September is the month to get rodent stations in place. Getting ahead of the move-in is dramatically easier than evicting them later.

October

Peak overwintering month. Box elder bugs, stink bugs, Asian lady beetles and cluster flies all pile into siding, window frames and attic vents.

They aren't damaging anything. They're just going to be in your living room in February if nothing gets treated now.

Mosquito season winds down through mid-to-late October depending on the first hard freeze.

November

Mice are in. If there's a gap, it's been found.

Everything that overwinters has settled into the structure. Exterior pest pressure drops off, which is exactly why people cancel service in November and then have a problem in February.

December

Quiet outside. Indoor rodent activity climbs as established populations breed. Occasional spider sightings in basements.

Nothing dramatic happens in December, and that's the point. What you did in September and October decides what December feels like.

Why quarterly service tracks this calendar

The products we use hold for roughly 90 days. Four visits a year, timed to the shoulders of each pressure season, means the barrier is freshest right when it needs to be.

That's the whole logic of Home Shield. Not spraying more, spraying at the right time.

Add Rodent Guard if you back to woods or a field, and mosquito and tick treatments from April through October if you actually want to use your yard.

Frequently asked questions

When should I start pest control in St. Louis?

March is ideal. Starting in March gets a barrier down before spring ant and spider pressure builds, so you're preventing rather than reacting. That said, any month works. If you have activity right now, that's the month to start.

What is the worst month for pests in St. Louis?

May and August, for different reasons. May is peak ant activity and August is peak wasp aggression. September is the most important month to act, because that's when rodents start moving indoors.

Do I need pest control in the winter in Missouri?

Yes, and winter is when skipping it shows up. Mice, spiders and overwintering insects are active inside your walls all winter. Homes that stay on service through winter start spring with far less pressure than homes that pause in November.

When does mosquito season start in St. Louis?

Early to mid April, once nights stay above about 50 degrees. Season runs through mid-to-late October depending on the first hard freeze, which is roughly nine treatments across a season.

Want the barrier down before the next season starts? Get a free quote or call us at (314) 912-2929. We'll tell you what we'd actually do at your address.