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Why yellowjackets get worse in late summer, and what to do about a ground nest in Cambridge
In June a yellowjacket nest is small and quiet. By late August the same colony can be thousands strong and working every garbage can and patio table in the yard. Here is what changes, and how to handle a nest in the lawn or a wall.
Last updated September 25, 2026 · Reviewed by the Cambridge Pest Control team
The yellowjackets in a Cambridge yard
The Royal Ontario Museum identifies the German wasp and the common yellowjacket as the two most common yellowjackets in Ontario. Both are social wasps that build a paper nest, and the Museum notes that queens start nests in wall spaces, tree stumps and underground. That matches what turns up in Cambridge: ground nests in lawns and gardens on the newer lots toward Blair and in the townships around Ayr, and wall-void nests behind siding and in soffits in Preston bungalows and Hespeler frame houses.
Why late summer is the worst of it
The colony follows a yearly cycle, as the Royal Ontario Museum describes it:
- Spring. A single queen that survived the winter starts a nest on her own and raises the first workers.
- Early summer. The workers take over gathering food, much of it insects fed to the growing larvae, and the nest expands quickly.
- August. The queen slows her egg laying and the colony raises males and new queens. With fewer larvae to feed, workers are free to forage for themselves, and they turn to sugar: pop, juice, fruit, and meat at barbecues.
- Fall. After the first frost most workers die, and none survive an Ontario winter. The new queens overwinter in a sheltered spot and start new nests the next spring.
So the late-summer picnic problem is a large colony at peak size with workers looking for sugar. The Museum also notes that a threatened yellowjacket can release chemicals that call nest mates to defend the colony, which is why disturbing a nest at this time of year can produce many stings at once.
Finding the nest
- Ground nests. Watch the lawn or garden bed from a distance on a warm afternoon. A steady line of wasps flying low into and out of a single hole, often under a shrub, at the edge of a patio or in an old rodent burrow, is the entrance.
- Wall voids. Wasps going in and out of a gap in siding, a soffit vent, a gap around a dryer or bathroom fan hood, or a weep hole in brick. A chewing or rustling sound inside the wall is a sign the nest is large.
- Exposed nests. Grey paper nests in shrubs, under eaves or in a shed are the easiest to spot and to deal with.
Mark the spot and keep people, pets and the lawn mower away. Running a mower or string trimmer over an unseen ground nest is one of the most common ways people get stung repeatedly.
Keeping the yard less attractive
Late-season workers are hunting for sugar and protein, so the practical steps are about food. Keep lids on garbage and green bins, rinse recycling, pick up fallen apples and pears, cover drinks outdoors, and clean the barbecue after use. Hummingbird feeders and open pet food on a deck also draw them in.
What not to do
- Do not pour gasoline or other fuels into a ground nest. It is a fire and contamination hazard and it is not a pest control product.
- Do not block the entrance of a wall-void nest from outside while the colony is active. The wasps look for another way out, and in a wall that can mean into the house. Entrances are sealed after the colony is dead.
- Do not knock down a large nest by hand or with a hose.
What Ontario's pesticide rules allow
Ontario's cosmetic pesticide ban restricts many products on lawns and gardens, but the province's own guidance lists wasps among the exceptions for health and safety. A nest near a door, a deck, a play area or a walkway is a legitimate reason to treat. Any product used at home must be used exactly as the label directs, and leftover product goes to household hazardous waste, not the garbage or a drain.
Wait for frost, or deal with it now?
Because the workers die with frost, a nest high in a tree at the back of a large lot that nobody goes near can be left alone. The new queens leave to overwinter elsewhere and start fresh nests in spring. Waiting makes less sense when:
- The nest is next to a door, a deck, a play structure or a path people use every day.
- Someone in the house has a known allergy to stings.
- The nest is in a wall void and wasps are showing up inside the house.
- The nest is in the lawn and the grass still has to be cut.
Bees are a different case
Honey bees and bumble bees are not yellowjackets, and a honey bee swarm or colony is handled differently. If you are not sure which insect you have, a photo taken from a safe distance helps. For yellowjacket, hornet and paper wasp nests in soffits, walls and the ground, see wasp and bee nest removal. Planning ranges for exposed and hidden nests are on the Cambridge pest control cost guide. To book a visit, use the contact page.