Seattle Pest Calendar: What to Watch Each Month

How should I use a pest calendar?

As a prompt to look at the right places in the right months, not as a prediction. Warm or wet years move every date, and a pest can appear outside its usual window. Rows backed by Washington State University or the Department of Health are marked, and the rest is common experience from the trade.

A calendar earns its keep by changing what you check. Looking at eaves in spring, bins and drinks in late summer, and crawl spaces and gaps as the rains return is more useful than a general worry about bugs.

The table below summarizes the year. Each row names its basis, so you can weigh the claim. Sections after it add detail.

What happens from January to March?

The wet season is under way, and the pest picture is mostly about damp wood and animals seeking shelter. Moisture ants, carpenter ants and dampwood termites look for wet or decayed wood, and rodents are heard in walls and crawl spaces. These are general concerns, not measured ones. It is a good time to check the crawl space for moisture.

Roughly three-quarters of the year's rain falls between about October and March, according to local weather reporting, and Sea-Tac's 1991 to 2020 normal is about 39 inches a year. Shaded wood stays wet, and north walls, decks and window sills take the brunt.

A winter look at the crawl space is useful, if the space is accessible and safe. Look for wet insulation, a torn vapor barrier, standing water and new droppings. If you find any, see moisture ant control and rodent exclusion.

This is also the season to plan the year. If last summer brought a wasp nest or a spring ant swarm, tell a technician and ask what to check before it returns. A short list of the likely spots, such as the eave, the sill and the stump, makes the next check quick.

What happens from April to early June?

Carpenter ant swarming, according to WSU PestSense. Winged males and females leave the nest, and winged ants appearing indoors in spring may mean a nest in the building. This is also the time to check eaves, sheds and gaps for early wasp nests, since each nest begins small with a single queen.

Ants are the main spring concern. A swarm on a window sill is worth identifying, because winged termites can look similar, though dampwood termites swarm later in the year. Capture one in a jar if you can.

It is also a good moment to do the simple prevention WSU lists: remove stumps and rotting logs near the house, keep branches off the eaves and fix damp wood. For the species, see the guide on carpenter and moisture ants.

Spring is also the moment to look for the first signs of wasps. A queen starts a nest alone, and a nest the size of a walnut under an eave is far easier to deal with than a late-summer colony. Ask for advice before disturbing one, especially if it is in a wall or the ground.

What happens from June to July?

Summer in the Seattle area is comparatively dry, with July averaging under an inch of rain at Sea-Tac, so pests shift to water and food. Ants come to leaks and sprinklers, mosquitoes breed in gutters and containers, and wasp colonies grow. These patterns are common experience, with colony growth described by WSU.

Dry weather can send ants indoors in search of water, so a slow leak under a sink is a draw. Standing water in a gutter or planter saucer can breed mosquitoes within days.

Mosquitoes here are mainly a nuisance. The Washington Department of Health's 2025 West Nile table, as we read it, listed no positive mosquito samples for King County, but surveillance is limited. See mosquito control for the yard checklist.

Outdoor living is at its peak, which is why wasps and mosquitoes seem to arrive all at once. A weekly walk around the yard to empty containers and a look at the eaves for early paper nests are small habits that pay off through August.

What happens from August to October?

Yellowjackets are most troublesome in August and September according to WSU, and the German yellowjacket reaches its peak colony size from October to early November. Dampwood termites swarm in late summer or fall, especially after rain. This is the busiest period for stinging insects, and the first rains often bring swarms.

Cover food and drinks outdoors, keep bins closed and clear fallen fruit. If a nest is near a door, deck or play area, call; WSU recommends professional removal near people and advises against swatting. Our guide on yellowjackets in the Seattle area has the detail.

After the first heavy rain, a flurry of winged insects may be termites. Keep a specimen, and see termites in western Washington before deciding it is serious.

Autumn is also the time to put the house in order before the rains. Clear gutters, extend downspouts, stack firewood away from walls and off the ground, and look at crawl space vents. These are the jobs that keep damp-wood pests and rodents from settling in over winter, and they cost far less than a repair.

• Cover food and drinks outdoors
• Check eaves, decks and the ground for nests
• Keep a specimen of any winged insects
• Note the date and weather of any swarm

What happens from November to December?

The wet season is back, with storms, and homeowners tend to notice rodents in walls and attics and damp-wood problems indoors. No local figure is published for either, so treat the pattern as experience. A look at gutters, the roofline and the crawl space before the heaviest rain is the best preparation.

December 2025 brought atmospheric river flooding to the Cedar River near Renton and the Cascade foothills, according to news reports, though no effect on pests is documented here. Floods and heavy rain affect crawl spaces and can leave wood wet for a long time.

If you notice new sounds in the walls or droppings in the garage, act promptly. See rat control and mouse control, or the guide on rats in Seattle.

How does weather shift the dates, and what is not on the calendar?

A warm spring brings swarms earlier, a wet autumn extends damp-wood trouble and a cold snap can end a wasp colony sooner. Indoor pests such as cockroaches and bed bugs follow buildings and travel, not seasons, so they are not tied to a month. Treat every date here as approximate and expect exceptions.

The same month can look very different from one year to the next. WSU gives windows, not deadlines, and a pest can show up before or after its usual dates.

Some pests simply do not belong on a calendar. Cockroaches live in heated buildings and spread through shared walls, and bed bugs ride on people and furniture. Spiders follow the insects they eat. For those, the useful habit is to check when you see a sign. See cockroach control and bed bug treatment for how those jobs run.

Squirrels and raccoons are wildlife, and the rules for handling them are set by the state, not by a pest calendar. Sealing the roofline in any season is the practical step; see squirrel and raccoon exclusion.

How do I turn this into a yearly routine?

Three checks cover most of it: spring for ants and early nests, early autumn for wasps, swarms and gutters before the rains, and winter for the crawl space and signs of rodents. Add a look whenever you notice a leak, a new sound or an unfamiliar insect. A routine takes an hour or two a year.

Write the dates on a calendar. The spring check is eaves, sheds and window sills; the autumn check is gutters, downspouts, firewood, crawl space vents and stumps; the winter check is the crawl space, attic hatch and garage for droppings.

If you rent, report what you find in writing to your landlord or manager. In apartments, a pest in one unit often means others have it too.