The biology behind the season
BC wasp colonies are annual, not perennial. Every colony dies in fall. Every nest you see in August was built from scratch by a single queen who overwintered and emerged in spring. Understanding the biology of the annual colony cycle is the most useful frame for understanding what to expect each month and when to act.
The queen overwinters as a mated female in a sheltered, insulated location — under bark, in wall cavities, in attic insulation, under leaf litter. She does not overwinter in the nest. The nest is abandoned in fall and never reused. When spring temperatures consistently exceed approximately 10°C, the queen emerges, begins feeding on carbohydrates (nectar, tree sap), and scouts for a nesting site. She builds the first cells of the nest alone, laying her first eggs — all of which will become sterile workers — and feeds the first larvae with chewed-up arthropods. Once those workers emerge (4-6 weeks after colony start), the queen stops foraging and nest-building and shifts to full-time egg-laying. From that point, the colony grows at a rate driven by ambient temperature and food availability.
| Month | What's happening | Risk level | Action for homeowners |
|---|---|---|---|
| January–February | Queens overwintering in sheltered cavities. Zero active colonies. | None | Plan prevention work for March |
| March | First queens emerge on warm days (above 10°C). Scouting for nest sites. No workers yet. | Very low | Apply preventive residual treatment to eaves, soffits, deck underside before nests establish |
| April | Queen building first nest cells solo. Nest is thumbnail to golf-ball size. First workers emerge late April. | Low | Last month for safe preventive treatment. First reports of nests — manageable if small paper wasp |
| May | First workers foraging. Colony 20-100 workers depending on weather. Nest grows visibly. | Low-moderate | Early nests discoverable now. DIY treatment possible for small accessible paper wasp nests only. |
| June | Colony growth acceleration. 100-400 workers by end of June. Nests become visible at bald-faced hornet size. | Moderate | Any yellowjacket or bald-faced hornet nest now requires professional treatment. Paper wasp at high-traffic locations: treat now. |
| July | Peak growth phase. Yellowjacket colonies reach 500-1,500 workers. Bald-faced hornet nests football-sized. High sting risk. | High | All active nests in residential areas: professional treatment immediately. No DIY. |
| August | Colony peak + scavenging shift. Largest colonies. Workers food-scavenging at outdoor areas. Highest human conflict. | Very high | Peak callout month. Priority booking for all nests. Outdoor food hygiene critical. EpiPens essential for high-risk households. |
| September | Colony decline begins. Queens producing new queens and male drones, not workers. Colony defensive, no new workers. | High-moderate | Still dangerous — treat all active nests. Outdoor activity still high-risk near food. |
| October | Colony death as temperature drops. Old workers die. New queens disperse to overwinter. Nest abandoned. | Low | Found nest with zero activity: safe to remove mechanically at any time after October 15 in most years. |
| November–December | No active colonies. Nests are empty, inert paper structures. | None | Safe to remove old nests. Plan prevention for March. |
March–April: the prevention window
The single most cost-effective intervention in the wasp season calendar happens in March and early April, before any queen has established a nest on your property. A residual pyrethroid application to the surfaces where wasps build — eave undersides, soffit interiors, deck joists, fence caps — discourages scouting queens from starting a nest in that location. This doesn't kill anything; it creates a chemical environment that queens avoid during the brief nest-selection phase. Once a colony is established (May onwards), this treatment has no effect on the existing nest. Homeowners who want to minimize the likelihood of a summer nest without ongoing professional intervention should schedule a preventive spring treatment.
May–June: small nests, large decisions
May is the month when most Metro Vancouver homeowners first discover nests they couldn't see in April. By late May, a paper wasp nest may be 5-10 cm in diameter with 20-50 workers — manageable for DIY under the right conditions. By mid-June, yellowjacket colonies reach 100+ workers and bald-faced hornet nests are clearly visible. June is the last month where removal of most species can be planned without an emergency-level approach. Leaving a June yellowjacket nest to address in July is consistently the decision homeowners regret most in our service records — a June nest of 150 workers becomes an August nest of 1,200 workers with a 5-metre defensive perimeter.
July: the colony explosion
July is when the BC wasp season shifts from manageable to urgent. The combination of peak temperature (which accelerates wasp metabolism and brood development), established colonies with hundreds of workers, and the fact that the queen's first brood cohort is now fully operational creates the conditions for rapid colony growth. In a good (for wasps) BC summer, a yellowjacket colony that had 300 workers on July 1 can have 1,000 workers by July 31. This is also the month when bald-faced hornet nests in trees and eaves reach the size where they become visible to homeowners who previously hadn't noticed them. July callouts for same-day service are our highest volume month, and the most common booking pattern is: 'I noticed it three weeks ago and decided to wait and see.'
August: the food-scavenging shift and peak conflict
August is the month of maximum human-wasp conflict in Metro Vancouver, driven by a specific biological event: the colony's brood-rearing phase winds down. Through spring and early summer, workers forage primarily for protein (insects, caterpillars, meat) to feed the brood. In August, the queen begins producing new queens and male drones rather than workers — and these require more carbohydrate than protein. Workers that were previously carrying insect protein to the nest are now food-scavenging for sugars: fruit, soft drinks, beer, barbecue sauce, garbage juice. This is the yellowjacket in your beer, in your open pop can, hovering over your fruit salad. These wasps are not protecting a nearby nest — they're individual foragers from a nest potentially 300 metres away. They sting when trapped (in drink cans, in hand when squeezing fruit) or swatted. The injury scenario that most commonly triggers anaphylaxis assessment in BC — the sting in the mouth or throat from a wasp in a drink can — peaks in August.
September–October: decline and last-season work
September brings the beginning of colony decline. The queen has shifted entirely to producing new queens and males. No new workers are being raised. The existing worker population ages and shrinks. But the remaining workers are not docile — late-season colonies are often more aggressive than mid-season ones, possibly because worker-to-nest ratio has changed and fewer workers are available to defend a large nest structure. October, with first frost events and temperatures dropping below 10°C, sees rapid colony death. Workers die off. New queens disperse to overwinter. By mid-October in most Metro Vancouver years, the season is effectively over. Old nests can be removed mechanically without pesticide application from mid-October onwards, once confirmed inactive by 48 hours of observation on a warm afternoon.