Rats in Longueuil After Spring Flooding — What Homeowners Need to Know

Every spring in Longueuil, the same phenomenon plays out along the St. Lawrence River and the Rivière Richelieu: snowmelt and spring rains raise water levels, flooding the underground burrow systems that Norway rats (Rattus norvegicus) have spent the winter building. Displaced from their burrows, these rats — sometimes thousands of them — move rapidly inland, seeking higher ground and new shelter. For homeowners in Longueuil's riverside neighbourhoods, this annual migration represents a significant and predictable pest pressure event.

This is not a random or unpredictable problem. It happens every year, in the same neighbourhoods, at the same time of year. Understanding the pattern allows homeowners to take preventive action before the rats arrive — which is dramatically more effective and less expensive than dealing with an established infestation.

Why Spring Flooding Drives Rats Into Longueuil Homes

Norway rats are burrowing animals. Their primary habitat is underground — in burrow systems that can extend 1–2 metres deep and several metres horizontally. These burrows provide shelter, nesting space, and food storage. When spring flooding raises the water table and inundates these burrows, the rats have no choice but to abandon them and find new shelter above ground.

Longueuil's geography makes this problem particularly acute. The city sits on the south bank of the St. Lawrence, with significant portions of the municipality at or near river level. The neighbourhoods of Vieux-Longueuil, Saint-Hubert, and the areas along the Rivière Richelieu are especially vulnerable to spring flooding — and to the rat displacement that follows.

Signs of Rat Activity in Your Longueuil Home

Norway rats are larger and more destructive than house mice. Here's what to look for:

• Droppings: Norway rat droppings are 12–20 mm long, dark brown, and blunt at one end. They are significantly larger than mouse droppings (3–6 mm). Fresh droppings are dark and moist; older droppings are grey and dry.
• Burrow entrances: Look for smooth, round holes (5–8 cm diameter) in the soil around your foundation, under concrete slabs, and along fence lines. Fresh burrows have loose soil at the entrance.
• Gnaw marks: Norway rats gnaw constantly to wear down their incisors. Look for gnaw marks on wood, plastic pipes, electrical cables, and food packaging. Rat gnaw marks are larger and rougher than mouse gnaw marks.
• Grease marks: Rats follow the same pathways repeatedly, leaving dark grease marks along walls, pipes, and beams from the oil in their fur.
• Sounds: Scratching, gnawing, and movement sounds in walls, under floors, and in the basement — particularly at night.
• Nests: Shredded paper, fabric, and insulation in hidden locations — behind appliances, in wall voids, under concrete slabs.

The Most Vulnerable Properties in Longueuil

Not all Longueuil properties are equally at risk. These factors increase vulnerability:

• Proximity to the St. Lawrence or Richelieu: Properties within 500 metres of the river are at highest risk during spring flooding events.
• Older construction: Homes built before 1970 typically have more foundation cracks, deteriorated mortar joints, and gaps around utility penetrations that provide rat entry points.
• Basement apartments: Ground-level and below-grade living spaces are more accessible to rats entering from the exterior.
• Attached garages: The gap under garage doors and the wall between the garage and living space are common rat entry points.
• Compost and garbage: Properties with outdoor compost bins, unsecured garbage, or bird feeders provide food sources that attract and sustain rat populations.
• Dense vegetation: Overgrown gardens, dense shrubs, and wood piles near the foundation provide cover for rats approaching the structure.

Immediate Actions If You Suspect Rats

If you find signs of rat activity in or around your Longueuil home, act immediately. Norway rats reproduce rapidly — a single pair can produce 40–60 offspring per year — and an infestation that starts with a few displaced rats in April can become a serious problem by June.

• Do NOT use poison bait stations without professional guidance: Improperly placed rodenticide can harm children, pets, and wildlife. It can also cause rats to die in inaccessible locations inside walls, creating odour problems.
• Do NOT seal entry points before eliminating the existing population: Sealing rats inside your home creates a desperate, destructive situation as they try to escape.
• Do remove food sources immediately: Secure all garbage in bins with tight-fitting lids, remove bird feeders, and store pet food in sealed metal containers.
• Do document what you find: Photograph droppings, gnaw marks, and burrow entrances. This helps the exterminator assess the severity of the infestation.
• Do call a professional: Norway rat infestations require professional treatment. DIY snap traps can reduce the population but rarely eliminate an established colony.

Professional Treatment for Rats in Longueuil

Professional rat control in Longueuil involves a two-phase approach:

• Phase 1 — Elimination: A strategic network of snap traps and tamper-resistant bait stations is installed in confirmed activity areas — along walls, near burrow entrances, and in the basement. Bait stations are secured to prevent access by children and pets.
• Phase 2 — Exclusion: Once the existing population is eliminated (typically 2–3 weeks), all entry points are sealed with professional-grade materials: steel wool, hardware cloth, hydraulic cement, and metal flashing. This prevents new rats from entering.
• Follow-up monitoring: A follow-up visit 2–4 weeks after the initial treatment confirms that the infestation has been eliminated and that no new entry points have been created.

Long-Term Prevention for Longueuil Homeowners

• Inspect your foundation every fall and seal any new cracks or gaps before winter
• Install door sweeps on all exterior doors, including the garage door
• Replace worn garage door bottom seals
• Keep vegetation trimmed back from the foundation
• Store firewood at least 6 metres from the house, elevated off the ground
• Eliminate outdoor food sources (bird feeders, unsecured compost, pet food)
• Consider a preventive perimeter treatment in March before the spring flooding season