Yellowjackets and Wasps in the Seattle Area: Why Late Summer Is the Risky Window

Why are yellowjackets worst in late summer?

Because their colonies are at peak size. WSU says each colony starts from a single overwintered queen in spring and grows through the summer, and that August to September is when yellowjackets are most troublesome. Workers also shift from hunting insects to seeking sugary food, which brings them to people, picnics and garbage bins.

The annual cycle explains most of what people notice. In spring a queen builds a small nest and raises the first workers. Those workers take over, the nest expands and by late summer the colony may number in the thousands. The wasps that were scarce in June are suddenly at every table.

The German yellowjacket reaches its peak colony size later, from October into early November, which is why a nest can still be a problem after the first rains. Cold finally ends the colony, and the old nest is not reused.

What kinds of wasp will I meet?

Mostly yellowjackets, which nest in the ground or in voids and scavenge at food, and European paper wasps, which build open-comb nests on structures and are common in urban areas, according to WSU. Hornets and bees are other possibilities. Identification from the nest and the insect comes before any decision.

A paper nest with an open honeycomb of cells under an eave usually points to paper wasps. A hole in the ground with a steady stream of wasps usually points to yellowjackets. A closed, grey, ball-shaped nest hanging from a branch may be a hornet. Our page on hornet nest removal covers aerial nests.

Bees are different from wasps. Honey bees and many native bees are not treated as pests, and a technician or a beekeeper can advise if bees are the problem.

For the homeowner, the practical question is whether a nest is active and near people. An abandoned paper nest in winter is just paper. A busy one beside the front steps in September is not. Photograph the nest from a distance and note how many wasps you see in a minute, which gives a technician a useful sense of its size.

If you are unsure whether insects are wasps, bees or flies that mimic them, wait for the specimen to be identified. Many harmless hover flies wear yellow and black, and removing the wrong insect helps no one.

Where do yellowjackets nest around a house?

In the ground, in rodent burrows and under stumps, in wall voids and attics, and under decks and eaves. WSU warns that ground nests in wall voids or attics can chew into rooms. Yellowjackets often use small openings, so a stream of wasps entering a crack in siding is a nest sign, not a visit.

Ground nests are the ones that people find by accident, when a mower, a trimmer or a child's foot passes over the entrance. Do not block the hole or pour anything into it. A disturbed colony defends itself in force.

Wall and attic nests announce themselves by a buzzing sound, a brown stain on a ceiling or wasps appearing indoors. Those cases are especially suited to a professional, because the nest may need treatment from inside the structure.

The Seattle area offers plenty of sheltered ground. Banks along ravines and lakeshores, old stumps, abandoned rodent burrows and the base of hedges on the lake suburbs and Eastside lots are the kind of places yellowjackets use. Dry summers help colonies thrive, and the months after the rains return are when the late nests of the German yellowjacket become noticeable.

• A steady stream of wasps at one hole in the ground or a bank
• Wasps entering a crack in siding, a vent or a soffit
• A buzzing or scratching sound in a wall or ceiling
• A grey paper nest under an eave, in a shrub or on a fence
• Wasps appearing indoors near a window

When should I leave a nest alone, and when should I call?

Leave it alone if it is small, far from people and not in use; call if it is near a door, deck, play area or path, in a wall or the ground, or if anyone is allergic. WSU recommends professional removal for nests near where people live and says not to swat. About one to two percent of people are severely allergic.

An empty paper nest in winter is harmless. A small, early nest the size of a walnut is easy to deal with but still best approached with advice. A busy nest at head height beside your back door is a call.

Phones here are answered 24/7, and a same-day visit is offered only when a technician is free. No arrival time is promised. Until then, keep children and pets away and stay clear of the entrance. See yellowjacket and wasp removal for how a visit works.

In an apartment or townhome, a nest under a shared balcony or in a common soffit is usually the landlord's or association's to arrange. Tell management in writing, note the location and keep children away until it is dealt with.

How does a technician deal with a nest?

The technician identifies the wasp, locates the nest and its entrance, wears protective clothing and applies a labelled product, usually when most workers are inside, such as at dusk. Wall and attic nests may need treatment from several sides. You are told how long to keep children and pets away and what repair, if any, is needed.

Expect questions first: where are the wasps going in, how many do you see, has anyone been stung, and is anyone allergic? The answers decide how urgent it is and what equipment to bring.

Afterwards, entrances are closed where practical and the nest is removed if it is accessible, which keeps scavengers from returning. Wasps that were foraging away from the nest may keep returning for a day or two, so some activity at the spot afterwards is normal. The price is confirmed with you before work starts, and nothing about the outcome is promised.

What do I do if someone is stung?

Move away from the nest, wash the area and apply a cold pack. Watch for signs of a severe allergic reaction, such as swelling of the face or throat, trouble breathing, dizziness or widespread hives, and call 911 if they appear. Multiple stings from a disturbed nest also warrant medical attention, especially for children and older adults.

Do not try to remove the nest while someone is hurt. Get people indoors and deal with the nest later with help.

People who know they are allergic should keep their prescribed medication at hand during the season and tell the technician before any work near their home.

Keep an eye on children in particular, who may not report a sting or may panic. Teach them to walk away calmly from wasps and not to swat or run through a nest area. At picnics, a quick check inside a cup or can before drinking is a habit worth teaching early.

How can I cut down yellowjacket trouble around the house?

Cover food and drinks outdoors, keep garbage in tight-lidded bins, clear fallen fruit, check eaves and sheds in spring for early nests and close gaps in siding. These steps make a property less attractive but cannot stop a queen from nesting nearby. A quick look in April and May is time well spent.

Late-summer outdoor meals are the flashpoint. A can of soda left open attracts yellowjackets, and one can hide a wasp. Pour into a cup, or use a lid and look before drinking.

If you see a few wasps going repeatedly to the same corner of the yard, follow them from a distance to find the nest. Note the spot and keep away. The sooner it is dealt with, the smaller it is.

Do removed nests come back?

Colonies are annual, according to WSU, and old nests are not reused. A new queen may nest in the same area the next year, particularly if the site is sheltered and gaps remain. Closing openings in soffits and siding and checking eaves in spring lowers the chance but cannot remove it.

If you have had a nest in the same place two years running, tell the technician. There may be a feature that makes the site appealing, such as a gap or a warm south-facing wall.

A follow-up check in spring is a good habit. Catching a nest when it is small saves work later.