The short version
Around Ontario, queens start nests in April, and colonies peak in late summer. Small, low paper wasp nests can be handled at dusk. Leave wall, ground and high nests to a pro.
- Treat nests at dusk, when wasps are home.
- Never seal a hole wasps are using.
- Ground and wall nests are best left to a pro.
- Knock down small nests early in spring.
- Call 911 for breathing trouble after a sting.
Homeowners and renters in Ontario with a nest near a door, deck or play area.
What to look for
Late-summer colonies are big and quick to sting. Near a door or deck, stings will happen. Wasps defend the area around their nest.
- 1Wasps appearing indoors near light fixtures or windows.
- 2Yellowjackets crowding trash cans, soda cans and pet food.
- 3Steady wasp traffic in and out of one soffit gap.
- 4Wasps disappearing into a hole in the lawn or a wall.
- 5Dead wasps collecting on interior windowsills in late summer.
- 6Wasps flying straight lines to and from one spot.
Why it’s worth acting soon
- Nests grow all summer.
- Ground nests get disturbed by mowing.
- Wall nests can chew through into rooms.
- Stings are dangerous for anyone allergic.
Treatment options and typical costs
Inspection and Nest Identification
$75–$200
The inspection also flags anyone in the Ontario household with a sting allergy, which changes how and when the work gets done. Ask for photos of what was found.
- Time
- 45–75 minutes
- Best for
- Every job; species and nest location decide the method
Sealing Up After the Nest Is Dead
$150–$450
This is the step homeowners skip most often. Sealing the void after treatment keeps the next colony out.
- Time
- 1–2 hours
- Best for
- Sealing the gap once the nest is dead
Aerial Nest Treatment and Removal
$100–$400
High nests near rooflines in Ontario may need a ladder, a pole applicator or, occasionally, a lift. That access is what moves a quote toward the upper end.
- Time
- 30–90 minutes
- Best for
- Exposed paper wasp, hornet and bald-faced hornet nests
Ground and Wall-Void Nest Treatment
$150–$500
Yellowjackets nesting in Ontario lawns, retaining walls and old rodent burrows are treated by applying insecticidal dust directly into the entrance hole. Dust carries deep into the chambers as workers walk through it.
- Time
- 30–60 minutes plus a return visit
- Best for
- Yellowjackets in lawns, retaining walls, soffits and wall voids
Prices are typical published ranges. Ask what’s included before you compare quotes.
Once a nest is dead, screening and sealing gaps around pipes and vents keeps next year's queen from using the same opening.Which wasps live around Ontario.
They build open, umbrella-shaped combs under eaves and railings. Western yellowjackets nest in the ground and in wall voids. They cause most stings. Bald-faced hornets build big gray nests in trees and eaves. In mild winters around Ontario, some yellowjacket nests survive and grow huge. Leave those to a pro. Mud daubers build tube-shaped mud nests. They rarely sting. Paper wasps are the most common around Ontario.
Local wasps conditions in Ontario.
Across Ontario, the area is mostly urban, so wasps pressure can differ from one block to the next depending on how tight the entry points are and how much food, water, or shelter is close by. An inspection in Ontario usually starts outside and works inward, checking the foundation, gaps around doors and windows, and any moisture or clutter near the structure first. Knowing Ontario's seasonal timing lets you schedule treatment before the busy stretch rather than after it, which usually means faster service and a more accurate quote. A provider who works Ontario and California every day can point out the specific conditions that matter most here, and getting the scope, price, and follow-up terms in writing makes it easier to compare options. Ontario sits in a semi-arid climate, and that sets the pace for wasp activity here: mid-summer through fall (July-October).
An unscreened foundation vent is an easy way in for a yellowjacket queen. Wasps flying in and out of a vent all day are a sign of a nest inside.When they’re most active.
Nests die back with the first hard freeze, around November. Early spring is the easiest time to remove small starts.
Where they nest around houses here.
Look under railings, play sets and grills. Watch for wasps flying in and out of a gap. A ground nest looks like wasps streaming from one hole. Homes from Ontario out to Rancho Cucamonga and Fontana share the same favorite nest spots. Many homes in Ontario sit on slabs, so check eaves, the garage and patio covers first.
A year of wasps in Ontario.
- Winter: lows near 42°F in Ontario. Some nests keep going. - Spring: queens start new nests around April. Knock down small starts. - Summer: highs near 95°F in Ontario help colonies grow fast. - Late summer: peak season. Workers hunt sweets near people.
Wasp, hornet or bee?
- Honey bee: fuzzy and golden. about relocation. - Paper wasp: slim, long legs, open comb. - Yellowjacket: bright yellow and black, nests in the ground. - Hornet: larger, with a big closed paper nest. - Mud dauber: thin waist, mud tube nests. Rarely stings.
If you get stung.
Wash the sting and use a cold pack. An antihistamine can ease itching and swelling. 911 for trouble breathing or a swollen face or throat. If someone carries an epinephrine pen, use it. Move away from the nest first.
Keeping wasps away from the patio.
- Gaps: seal gaps after a nest is gone. - Food: cover plates and drinks outdoors. - Trash: keep lids tight and bins away from doors. - Fruit: pick up fallen fruit. - Spring checks: knock down small nests early.
Ground nests: what to do.
Keep kids and pets away. Don't mow over it. Don't pour gasoline or water in. Pros treat ground nests at night, when the colony is home. Mark the hole with a flag.
A nest, or just visitors?
A nest shows steady traffic to one spot. Watch at dusk, when they fly home. Follow the line back to an eave, vent, shrub or hole. Wasps on flowers or trash cans may come from far away.
Treating a small nest yourself, safely.
- Leave it overnight, then bag the nest. - Only if it’s small, low and out in the open. - Never if anyone in the house is allergic. - Wait until dusk, when wasps are home and slow. - Wear long sleeves, pants and gloves. - Use a jet wasp spray from several feet away. - Never spray from a ladder.
Wasps and pets.
Most stings just swell a little. your vet if the throat swells or breathing changes. Keep pet food and water bowls indoors in late summer. Dogs often snap at wasps and get stung on the face.
Kids and wasps.
Swatting makes a sting more likely. Check play sets, slides and playhouses for nests each spring. Use cups with lids for sweet drinks outside. Teach kids to walk away calmly.
After the nest is gone.
Seal the gap a wall nest used once it's quiet. Check nearby eaves for new starts. Knock down small new nests early next spring. Wasps don't reuse old nests.
Wasps at picnics and barbecues.
- Kids: teach them to walk away calmly. - Drinks: use cups with lids or straws. - Food: keep it covered until you eat. - Trash: bag scraps and close the bin. - Calm: don’t swat; slowly move away.
Ground nests in the lawn.
Watch for wasps flying in and out of the grass. Mark it, and keep mowers and kids away until it's treated. Yellowjackets often nest in old rodent holes.
Questions to ask before you sign.
- Is a return visit included? - What kind of wasp is it? - How will you treat a nest inside the wall? - Is removal of the dead nest included?
What affects the price
- Number of nests found on the property.
- Sealing gaps after the nest is dead.
- Dense siding, brick or stone that limits dust access.
- Return visit to confirm a void nest is dead.
- Whether nest removal is included after treatment.
- Nest height, and whether it needs a lift.
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What's your biggest concern about wasps?
When to call for help
They'll find another way in. Don't seal a hole wasps are using. right away if anyone in the house is allergic. Call for nests in walls, attics, the ground, or anywhere high.
What you can do yourself
A small, reachable paper wasp nest is a fair DIY job. Spray it at dusk with a wasp aerosol. Knock it down the next day. Big, high or hidden nests are a job for a pro.
Wasps in Ontario
Ontario only gets about 15 inches of rain a year, so local wasps often gather at pools, fountains and dripping taps. Winter lows near 42°F in Ontario are mild, so some yellowjacket nests survive the winter and keep growing. In denser parts of Ontario, nests turn up in eaves, balconies, signs and wall gaps.
Local research
Wasps in Ontario, CA: what the public record shows
Before you compare quotes, it helps to know which wasps actually live in California, when they are busiest around Ontario, and what the state figures look like. Everything below links to the agency or university page it came from.
Yellowjacket colony size (UC IPM)
A mature nest inside a wall void can hold thousands of workers.
UC Statewide IPM ProgramPaper wasp colony size (UC IPM)
Paper wasp nests under eaves are small and usually a quick single-visit job.
UC Statewide IPM ProgramWasp species recorded in California
- Western yellowjacket (Vespula pensylvanica) — UC IPM: 'the most commonly encountered species and is sometimes called the "meat bee"' in California and the Western states; ground and wall-void nester and aggressive scavenger…
- German yellowjacket (Vespula germanica) — UC IPM: 'becoming more common in many urban areas of California, where it frequently nests in houses.' Named among Ohio's three main species (German, Eastern, Common yellowjacke…
- Bald-faced hornet (Dolichovespula maculata) — Penn State: 'found in most of the 48 contiguous states and D.C., throughout Canada and in Alaska'; actually an aerial yellowjacket that builds the football-shaped gray paper nes…
- European paper wasp (Polistes dominula) — Penn State: 'first reported in 1978 around Boston', now 'coast to coast ... although they are apparently less common in the Southeast and Great Plains'; nests in 'eaves of struc…
When wasps are busiest around Ontario
Queens emerge in late winter to early spring, nests grow from spring to midsummer and peak in late summer; in coastal California south of San Francisco some yellowjacket colonies survive several years and become very large (UC IPM).
UC IPM: the western yellowjacket is the most commonly encountered species ('meat bee'); the German yellowjacket 'is becoming more common in many urban areas of California, where it frequently nests in houses.' Paper wasps (Polistes fuscatus aurifer, P. apachus, P. dominula) prefer orchards and vineyards.
Rules that apply in California
For context, nationally
- 788 — Deaths from hornet, wasp, and bee stings, 2011–2021 (US). CDC MMWR
- 72 deaths per year — Average annual sting deaths, 2011–2021 (US). CDC MMWR
Sources: Yellowjackets and Other Social Wasps (Pest Notes); CDC MMWR; Baldfaced Hornet; European Paper Wasp. Figures are quoted as the source prints them. How we check our sources
Simple ways to keep wasps away
- Screen attic, gable and dryer vents with fine mesh.
- Walk the eaves in April and knock down starter nests.
- Note where nests appeared and inspect there early next year.
- Cover drinks outdoors and use lidded cups for kids.
- Repair torn window screens and door sweeps.
Jot down where nests turned up this year. Queens often pick the same eaves and gaps, so you'll know where to look first next spring.Did you know?
Yellowjacket nests are never reused a second year
Some paper wasps can tell their nestmates apart by their faces
Questions people ask
Should I be worried about a nest in the ground?
Yes, if it's near a path or play area. Ground nests are usually yellowjackets. Mowing over them sets them off.
Can I seal the hole wasps are using?
No. Sealing traps them inside. They may chew into your house. Treat first, then seal once activity stops.
What time of day should a wasp nest be treated?
At dusk or after dark, when they're home and calm.
How do I know if I have wasps, hornets or yellowjackets?
Paper wasps build open, umbrella-shaped combs. Yellowjackets nest in the ground or walls. Hornets build big, gray, closed nests.
Why are there suddenly so many wasps in late summer?
Colonies are at their biggest by late summer. Food gets scarce, so workers hunt sweets and protein near people.
Is cost the main reason people leave wasp nests alone?
Not usually. More often the nest goes unnoticed or is hard to reach. A small, early nest is often cheap to remove.
How common are wasp sightings?
Across Ontario, very common in late summer, when colonies peak and wasps go looking for sweet food.
Are hornets common in Ontario?
Bald-faced hornets are, in trees and on eaves. Most stings come from yellowjackets, though.
Nearby cities
Related guides
Sources (9)
The facts in this article come from the public sources listed above. Every home is different, so ask the company you talk to about pricing and what’s included. Published by Wasp Exterminator · Updated September 11, 2026 · How we write these guides