The Seasonal Pest Calendar: What to Watch For All Year

Pest activity isn't random and it isn't constant. Every species has a predictable window when it peaks — driven by temperature, humidity, and reproductive cycles — and homeowners who know the calendar can head off most problems with a small amount of work in the right week. Here's what to expect month by month across most of the continental U.S. Adjust a few weeks earlier if you're in the deep South, a few weeks later if you're in the northern tier.

Late winter (February–March): the first swarms

As soon as overnight temperatures rise above about fifty degrees for a few days in a row, subterranean termite colonies release their spring swarmers. This is one of the two windows a year when you can catch a termite infestation you didn't know you had — piles of discarded wings on windowsills or around exterior lights are the giveaway. Carpenter ants also start moving. Fix any water leaks in the crawlspace or basement now, before the ground fully thaws and colonies get established.

Early spring (April): ants and rodents move

Ant colonies wake up hungry. The first indoor ant trails appear on kitchen counters and around pet food bowls. Mice that overwintered in walls and attics start looking to move back outside — you'll actually see more rodent activity briefly as they relocate. Clean out garages, sheds, and basements now while it's cool but before it's too muddy to work outdoors.

Late spring (May–June): mosquito and tick pressure spikes

Standing water from spring rains breeds the first mosquito generation. Tick populations peak in late May and June, particularly in yards adjacent to woods or tall grass. This is the moment to start a monthly mosquito and tick barrier program — starting in July is starting three generations late. Wasps and hornets begin building nests under eaves, in shrubs, and inside grill covers. Knock down small nests early before they become footballs.

Early summer (June–July): stinging insects and heat-driven roaches

Yellowjacket and hornet colonies grow explosively. By July, ground-nesting yellowjackets are a real hazard during lawn work. Roach populations — particularly outdoor species like American cockroaches — hit their peak and push into homes seeking moisture during hot dry spells. This is the highest-pressure season for pests in general and the worst month to skip a scheduled service.

Late summer (August): fleas, fruit flies, and drought pressure

Flea populations peak in late summer, driven by warm humid conditions. If you have pets and haven't been aggressive with monthly preventatives, this is when infestations blow up. Kitchen fruit flies explode with peak fruit and produce season. Ants become more aggressive because natural food sources dwindle — expect renewed indoor trails even if spring treatments went well.

Early fall (September–October): the great migration

The single most important pest-control month for most homes. As nights cool, every pest that overwinters indoors starts scouting for a way in. Mice, stink bugs, boxelder bugs, lady beetles, cluster flies, roof rats, and spiders all look for entry points. Exterior perimeter treatments and thorough exclusion (sealing, screening, door sweeps) done in September pay for themselves ten times over by January. Skip this month and you'll be dealing with what got in through March.

Late fall (November): rodents settle in

Whatever came in during October is now nesting in your walls, attic, or garage. This is when homeowners first hear scratching overhead at night. Rodent trapping and exclusion is the primary work of the month. Termite swarmers get a smaller second window in warm regions.

Winter (December–January): the quiet that isn't quiet

Cold weather doesn't stop indoor pests — it concentrates them. German cockroaches, bed bugs, silverfish, and drain flies all thrive in heated homes with minimal outdoor competition. Rodents already inside continue breeding. Winter is the season for interior-focused service: monitoring stations, kitchen and bathroom inspections, and follow-up on any fall activity. It's also the best time for major work like heat treatments for bed bugs, because the household disruption is easier when everyone's indoors anyway.

How to use the calendar

You don't have to do everything on this list every month. The pattern that works for most homes is a professional exterior treatment in early spring, monthly mosquito and tick service May through October, a serious exclusion pass in September, and an interior inspection in January. Everything else is opportunistic — a nest you spot, a leak you fix, a bag of birdseed you finally put in a metal can.

Pests operate on a calendar. Your defense should too.