Winter Pests in the Greater Toronto Area

Even in the winter, pest activity around the Greater Toronto Area sadly does not end instead it is concentrated even more. Any intruders that may have ventured into your home before the first hard frost hits is now denning it producing offsprings, causing damage (wiring, insulation, HVAC), and throughout the coldest months of the year. The indoor warmth makes GTA homes an ideal year-round habitat for serval species regardless of the outside temperature.

1. The Year-Round Resident: Mice (Active All Winter)

When the trifecta of warmth, food, and shelter are all present, the house mouse has no reason to slow down reproducing. A single female is sexually mature at six weeks and can produce a new litter every three weeks. The average litter size is 5-8 and an average female can have 5-10 litters a year. A colony of 2 can grow to between 25 to 80 in one year.

• The Warning Sign: Scratching or scurrying sounds inside walls and ceilings between 11 PM and 3 AM at night when mouse activity usually peaks. Fresh droppings seen near the water heater, under the kitchen sink, or in the back corners of cabinets confirm an active rodent infestation.
• The Risk: A pair of mice that entered in October can produce a colony of 20 or more individuals by February. The longer the infestation is left untreated, the more extensive the exclusion and remediation work required.

2. The Hidden Colony: Carpenter Ants (Dormant but Present)

Carpenter Ant satellite colonies established inside walls during spring and summer and but dormant during colder months. The first warm days of late winter can cause workers to become active and appear inside living spaces.

• The Warning Sign: Seeing a Carpenter Ant inside your home between November and February is highly significant. It almost certainly means a colony is overwintering within the heated envelope of the structure and not in a tree or stump outside.
• The Risk: Colonies resume full excavation activity in March. Each additional winter cycle means another season of structural damage inside house framing, window surrounds, or roof structures.

3. The Active Attic Tenant: Squirrels

Unlike raccoons, Eastern Grey Squirrels do not hibernate or enter torpor* state. They actually remain fully active through every winter relying on cached food stores and body fat to sustain them. A squirrel that gained attic access in the fall is generating damage continuously through January and February going undetected until the spring.

• The Warning Sign: Rapid light scurrying in the attic starting shortly after sunrise and in late afternoon. This daytime pattern is the clearest indicator that squirrels are present. Listen for gnawing sounds from the same location indicates a fixed chew site on framing or wiring.
• The Risk: Squirrel incisors grow approximately 15cm (6 inches) per year and must be constantly worn down through gnawing. Any attic wiring, plumbing pipes, HVAC ducting, and structural timbers are their targets. The damage discovered in spring is almost always more extensive than initial entry signs suggested because squirrels work quietly and methodically throughout the winter months.
• The Common Mistake: Many homeowners hear daytime attic sounds assume the problem will resolve once the weather warms and delay treatment until spring. By that point, a female squirrel may have already given birth to her first litter of the year as early as late February or March causing significant removal complications.

*torpor: decreased physiological activity in animals characterized by reduced body temperature, metabolism, heart rate, and respiration to conserve energy during harsh conditions or food shortages.

4. The Cold-Seeking Cluster: Overwintering Insects Emerging Early

On unexpectedly warm winter days in January where the Greater Toronto Area temperatures briefly reach above 10°C. The overwintering cluster flies, Asian lady beetles, and western conifer seed bugs inside wall voids can mistake the warmth for spring and begin moving toward light sources inside the home.

• The Warning Sign: Finding sluggish flies or slow beetles on interior window sills on mild winter days particularly on the south and west sides of the home. In the fall, the sun hits the south and west sides of structures for the most hours of the day making an ideal heat source for these insects.
• The Behaviour: These are the same insects that entered the wall voids in September. Their numbers typically increase in February and March as true spring approaches.

5. The Winter Pantry Pest: Stored Product Insects

The Indian Meal Moth, Red Flour Beetle, and Drugstore Beetle are active year-round pests found in heated GTA homes. Winter is when pantry pest infestations that began in fall are most commonly discovered after a holiday baking session reveals webbing in flour or small moths in the cereal cupboard.

• The Warning Sign: Fine silk webbing clumping flour, oats, or grain together inside packaging. Commonly found as small (3–4mm) reddish-brown beetles found in dry food containers. Indian Meal Moth adults flying in the kitchen at night are a reliable indicator.
• The Risk: Pantry moth larvae penetrate sealed factory packaging. Finding an infestation in one item means adjacent susceptible items are likely affected already. The entire pantry must be inspected and all affected items discarded.
• Introduction route: Most winter pantry pest infestations trace back to a single infested item purchased from a grocery or bulk food store during the holiday shopping period.

6. The Moisture Indicator: Silverfish in Winter Basements

Silverfish (Lepisma saccharina) are year-round indoor pests that become most visible in GTA homes during winter. During this season, residents will spend more time in lower-level living spaces and the difference between interior humidity and outdoor dryness creates condensation in basements, crawlspaces, and around cold-water pipes. Silverfish require high humidity (75–95%) and moderate warmth to thrive within a GTA basement.

They are one of the most ancient insects on earth. Silverfish have existed essentially unchanged for over 400 million years. Their survival is attributed to an ability to go without food for up to a year, their fast movement that makes them difficult to catch, and their preference for environments humans rarely inspect closely. Silverfish feed on starch, sugar, and protein. Their ideal food in these forms are paper, cardboard, glue, wallpaper, book bindings, and fabric sizing.

• The Warning Sign: Fast-moving, teardrop-shaped silver-grey insects approximately 15–20mm long with two long antennae and three bristle-like tails, seen moving quickly away from light when a basement light is switched on or a box is moved. Irregular holes and yellow staining on stored paper, books, wallpaper, and cardboard storage boxes. Small pepper-like droppings near food sources or in damp corners.
• The Risk: Silverfish can cause significant damage to stored documents, books, vintage clothing, wallpaper, and any paper-based packaging over time. A large winter population in a basement points to an underlying moisture problem. These moisture problems could potentially be a condensation issue, a slow leak, or inadequate vapour barrier likely leading to a source of mould growth and structural dampness that will become more serious in spring.

7. The Denning Tenant: Raccoons in Torpor

Raccoons do not hibernate but enter a state of torpor. Torpor is a shallow sleep characterized by reduced metabolic rate, heart rate, and body temperature that occurs during sustained cold snaps. A raccoon that established an attic den in October or November will typically be in torpor through the deepest cold of December and January, becoming more active again in February as temperatures fluctuate and as breeding season approaches.

The critical wildlife management fact about winter raccoons is what comes next: GTA raccoons breed from January through March, and females give birth in April and May. A raccoon in torpor in your attic in December is in the early stages of pregnancy by February. By the time a homeowner notices the resumption of activity in late February or March, a litter is typically already present or imminent which is a situation that significantly complicates removal and exclusion.

• The Warning Sign: Heavy thumping or dragging sounds in the attic at dusk and dawn during brief mid-winter warm periods when torpor is interrupted. A sudden new odour in the attic space, particularly a strong ammonia smell from urine-soaked insulation, indicates an established den with ongoing contamination. Fresh scratch marks on the exterior fascia visible during a roofline inspection in January or February.
• The Risk: A denning raccoon contaminates attic insulation with urine, feces, and parasites including Baylisascaris procyonis (raccoon roundworm), which poses a genuine health risk to humans and pets and is not destroyed by standard cleaning. Raccoon roundworm eggs can survive in soil and insulation for years. Contaminated insulation in most cases requires complete removal and replacement.
• The Timing: February is the last practical month to safely remove a raccoon from an attic before a litter is present. After March, removal requires ensuring all young are located and safely extracted before any exclusion work is done. Book an inspection in January if any raccoon activity was present in fall. We recommend acting on it before breeding season begins is considerably simpler and less expensive than acting after.

Winter Pest Prevention Checklist for GTA Homeowners

1. Perform a monthly inspection of kitchen cabinets, under sinks, and the utility rooms: Fresh mouse droppings are dark and moist with the older ones becoming grey and crumbled. Finding fresh droppings confirms ongoing rodent activity that requires immediate professional attention.
2. Check attic insulation through the hatch in January: Mouse runways and squirrel nesting depressions are visible with a flashlight and confirm activity levels without requiring a full attic entry.
3. Listen for daytime sounds in the attic: Rapid scurrying after sunrise means squirrels. Heavy thumping at dusk and dawn means raccoons. Light scratching late at night means mice. Identifying the species will determine the treatment approach.
4. Inspect all dry food storage after the holiday period: Check flour, oats, cereals, nuts, dried fruit, spices, and pet food for webbing, larvae, or live beetles. Transfer all clean items to sealed glass or hard plastic containers.
5. Monitor for Carpenter Ants on mild days: A single large black ant seen inside in January or February is worth a professional inspection because this sighting is rarely an isolated case.
6. Prepare for spring exclusion work in February: Book an inspection, order materials, and plan roofline exclusion work  before the March wildlife denning season opens and demand for pest professionals peaks. Squirrel litters begin as early as late February so early booking matters.