The Ottawa Fall Pest Checklist

As Ottawa's temperatures start dropping in fall, pest pressure doesn't disappear — it shifts. Every pest that spent summer outdoors starts looking for a warmer place to spend winter, and for many species, that means your home. Here's what to check for and address before the first hard frost.

Mice — The Single Biggest Fall Concern

Mice are by far the most common fall pest call in Ottawa, and for good reason: as outdoor temperatures drop, they actively seek indoor shelter, entering through gaps as small as 6mm around foundations, utility lines, and door thresholds. Fall is the ideal time for exclusion sealing, since it's addressing the problem before mice establish themselves rather than after.

Spiders Moving Indoors With the Cold

Spider sightings inside Ottawa homes typically increase through September and October as both spiders and the smaller insects they feed on seek warmth indoors. This is a seasonal wave tied to temperature, not usually a sign of a new infestation, though a perimeter treatment in early fall can meaningfully reduce how many make it inside.

Cluster Flies Seeking Overwintering Sites

Cluster flies specifically seek out buildings in fall to overwinter, often congregating in large numbers in attics, wall voids, or unused upper rooms. Unlike house flies, they don't breed indoors, but a large cluster fly population can become a persistent nuisance through winter and into early spring as they periodically become active on warm days.

Wildlife Seeking Denning Sites for Winter

Raccoons and squirrels both look for winter denning sites in fall, similar to spring but without the added complication of dependent young in most cases. Any new attic activity noticed in September or October is worth investigating before an animal fully settles in for the winter months.

Sealing Entry Points Before It's Too Late

Every pest on this list shares one thing in common: they need a way in. Fall is the single best time to inspect and seal foundation cracks, gaps around utility penetrations, damaged screens, and worn door thresholds, since this addresses mice, spiders, and wildlife risk simultaneously rather than treating each pest separately after the fact.

Why Waiting Until Winter Costs More

Once mice or wildlife are established indoors for winter, addressing the problem becomes more involved than prevention would have been — populations grow, and removal during cold months is more complex than exclusion work done while temperatures still allow easy access to the exterior. A fall inspection is consistently the more efficient time to act.

Frequently Asked Questions