Wildfire smoke season and indoor pest behaviour in BC: August–September patterns

BC's wildfire smoke season: the new normal since 2021

Before 2017, wildfire smoke in Metro Vancouver was a rare multi-day event. Since 2017, and especially since the June 2021 heat dome (which preceded a record fire season that burned 1.6 million hectares), the smoke season has become a predictable annual feature of BC summers. Metro Vancouver typically experiences 2–6 multi-day smoke events between late July and late September, with Air Quality Health Index values frequently exceeding 7 (High risk) during peak events. The 2021 heat dome saw Lytton reach 49.6°C before burning, and Vancouver itself reached 40.1°C — the highest recorded temperature in the city's history. These are not anomalies; they are the new baseline for summer pest planning.

How smoke affects pest behaviour outdoors

Insects navigate using visual and olfactory cues. Smoke substantially degrades both. Yellowjackets and other wasps rely on visual landmark recognition and airborne chemical trails to navigate foraging routes. During heavy smoke events, foraging activity reduces noticeably — we see fewer wasp calls during the worst smoke days of August and September. This is temporary and does not reduce wasp colony size; the colony simply hunkers down and reduces foraging range. When smoke clears, foraging intensity rebounds, sometimes with increased aggression as the colony makes up for the reduced-activity period.

• Flying insects (wasps, flies, aphids) reduce outdoor activity during active smoke events — visual navigation is impaired.
• Ant trail activity may temporarily increase as ants rely on pheromone trails rather than visual cues — smoke may disrupt above-ground orientation for some species.
• Spiders in exterior web locations may abandon webs during severe smoke events and seek sheltered locations.
• Wildlife (raccoons, deer, birds) that normally follow predictable patterns become more erratic during smoke events, potentially exploring new areas near structures.

How heat events drive pest ingress into structures

The heat events associated with BC wildfire seasons — not the smoke itself, but the high-pressure heat conditions that produce fire weather — have a direct and significant effect on indoor pest pressure. Metro Vancouver homes built before 2000 are generally not air-conditioned; the extreme heat events of BC summer create strong thermal gradients between the hot outdoor environment and the cooler interior of any building with shade and thermal mass. Insects and rodents follow the thermal gradient toward cooler spaces.

During the June 2021 heat dome, service call volumes for rodents in cooled commercial properties (grocery stores, restaurants, office buildings with A/C) increased dramatically compared to prior summers. The pattern has repeated in subsequent heat events. Rodents that normally forage entirely outdoors in summer begin probing structure entry points during sustained heat events above 35°C. Cockroaches in infested multi-family buildings move toward cooler stairwells and lower floors. Flying insects actively seek the cooler air near HVAC intake points.

Smoke season management protocol

• During active smoke events, postpone exterior perimeter applications — the product is less effective in reduced-UV, particulate-laden conditions and applicator health is also a concern.
• Monitor interior activity more closely during and immediately after smoke events — the behaviour disruption period produces atypical pest encounters.
• Keep doors and windows closed during smoke events — air sealing for air quality also reduces insect ingress.
• After a major smoke event clears, expect rebound wasp activity — schedule any pending wasp removal promptly as colonies resume full foraging.
• Inspect HVAC intakes and rooftop penetrations during heat events for evidence of pest probing.