Mouse vs Rat: How to Tell Which Rodent Is in Your London Home

The evidence matters before you treat. Mice and rats are managed differently — trap sizing, bait station placement, exclusion gap thresholds, and follow-up timelines all differ depending on which species is in your home. Getting it wrong wastes time and money.

Size: The Most Reliable Tell

If you've seen the animal, size settles it fast.

• House mouse (*Mus musculus*): 7–10 cm body length, tail approximately equal to body length. Weighs 12–30 grams. Large ears relative to body size. Pointed snout.
• Norway rat (*Rattus norvegicus*): 20–25 cm body length, shorter and thicker tail. Weighs 200–500 grams. Smaller ears relative to body size. Blunt snout.

In London, Ontario, Norway rats are by far the more common rat species. They're ground-dwellers that prefer to burrow near foundations, under concrete pads, and along water features. Roof rats (*Rattus rattus*) are rare in this region.

Droppings: Size and Shape Tell You Everything

Droppings are usually the first evidence homeowners find, and they're reliable for identification.

| | Mouse | Rat |

|---|---|---|

| Size | 3–6 mm | 12–20 mm |

| Shape | Pointed at both ends | Capsule-shaped, blunt ends |

| Location | Scattered widely — mice explore constantly | Concentrated near burrows and food sources |

Finding a mix of fresh (dark, moist) and old (grey, crumbling) droppings tells you how long the activity has been ongoing. Fresh droppings indicate current activity.

Gnaw Marks

Both species gnaw constantly to manage incisor growth, but the scale differs significantly.

• Mouse gnaw marks: Small, clean-edged holes in drywall, food packaging, and wood. A mouse needs a gap of only 6 mm to enter — about the diameter of a pencil.
• Rat gnaw marks: Much larger and more destructive. Rats chew through wood, soft concrete, and even thin sheet metal. Entry gaps for rats are 20 mm or larger. Rat-gnawed edges are rough and splintered.

Rats also cause considerably more structural damage and can gnaw through water pipes and electrical conduit.

Burrows vs Nests

• Mice build nests from shredded soft materials — paper, insulation, fabric — in hidden cavities. Common locations: inside wall voids, behind appliances, in drawer backs, inside insulation in crawlspaces.
• Rats burrow. Rat burrows are 6–9 cm diameter holes, typically found along the exterior foundation, under concrete pads or sheds, near compost bins, and along fence lines. An active burrow will have smooth, worn edges and fresh soil around the entrance.

In White Oaks and Westminster — neighbourhoods with older concrete work and established gardens — Norway rat burrows near foundations are a common call in late summer and fall.

Behaviour Differences

• Mice are curious and will investigate new objects placed in their territory within 1–2 days. This makes snap trap placement effective relatively quickly.
• Rats are neophobic — they avoid new objects for days or weeks. Bait stations placed near rat burrows or runways often need 3–7 days before rats interact with them. Rushing trapping without allowing habituation is a common reason DIY rat control fails.
• Mice move constantly and cover a home-range of about 3–10 metres from nest to food. Rats have a home-range of 30–100 metres and are more methodical travellers.

Treatment Implications

These differences matter for treatment design:

| Factor | Mouse | Rat |

|---|---|---|

| Entry gap threshold | 6 mm | 20 mm |

| Trap/bait station type | Small snap traps, enclosed bait stations | Large traps, tamper-resistant bait stations |

| Habituation period before trapping | 1–2 days | 3–7 days |

| Burrow treatment | Not applicable | Direct dusting or fumigation may be needed |

| Exclusion complexity | Moderate | Higher — rats are physically stronger and more persistent |

If you've found what looks like both large and small droppings, you may have both species simultaneously — uncommon, but it does happen in older homes with multiple access points.

For confirmed rat activity near the foundation or in a crawlspace, professional rodent control is the practical starting point. Exclusion work for rats is more extensive and the materials used need to withstand significantly more force than what deters mice.

Book a rodent inspection and we'll confirm the species, map the entry points, and design the right program.