Mouse or Rat? How to Tell From Droppings and Signs

You found small black pellets at the back of a cabinet or along a basement wall, and the question comes right away: mouse or rat? The answer changes the treatment, the entry point you need to find and how urgent the whole thing is. Mouse droppings and rat droppings look nothing alike once you know what to measure. Here are the sizes, the other signs to check, the safe way to clean up and the point where you should call.

What do mouse droppings look like compared to rat droppings?

Mouse. Mouse droppings are 3 to 6 mm long, the size of a grain of rice, black, with pointed ends. One mouse leaves 50 to 75 a day and scatters them everywhere it travels: along a baseboard, in the cutlery drawer, at the back of the pantry. Droppings up high are almost always mouse, because a mouse climbs anything. Our guide to the 10 signs of mice in the house lists the other spots to check.

Rat. The rat you meet in Quebec is the Norway rat, or brown rat. Its droppings are 15 to 20 mm long, three times the length, shaped like a capsule with blunt, rounded ends, like a fat raisin. A rat leaves 40 to 50 a day but groups them in piles at a few spots, at floor level: along a basement wall, next to a floor drain, in the garage or under a deck.

Between the two sizes, go by the shape: always rounded on a rat, always pointed on a mouse.

How can you tell if droppings are fresh or old?

Fresh droppings, under two days old, are black, glossy and soft. Press one with the tip of a pencil (never a finger) and it squashes like modelling clay. Droppings several weeks old are grey, dull and dry, and they crumble to dust.

To settle it, clean one spot completely and check again 48 hours later. New droppings mean the activity is ongoing.

What other signs separate a mouse from a rat?

When the droppings leave room for doubt, five other signs settle it.

Gnaw marks. A mouse leaves two parallel grooves 1 to 2 mm wide on cabinet corners and food packaging. A rat's grooves are 3 to 4 mm wide and much deeper, often in hardwood or hard plastic.

Grease marks. Fur leaves a dark smear where the animal rubs the wall on its usual route. On a mouse the line is thin and low, 1 or 2 cm off the floor. On a rat it is wider and darker and sits 5 to 10 cm up the wall.

Holes and burrows. A mouse fits through a 6 mm gap and does not dig. A rat needs at least 2 cm, the size of a quarter, and it digs. A hole 5 to 8 cm across in the soil along the foundation, under the deck or next to the compost bin, with fresh dirt at the entrance, is a rat burrow.

Footprints. Dust some flour along the suspect wall and look the next morning. A mouse hind foot is under 1 cm; a rat hind foot is 2 to 4 cm, with a wider tail drag.

Noises. A mouse makes short, light scratching with quick little footsteps. A rat is heavier and slower, and sometimes you hear the chewing itself. Our guide to scratching noises in your walls tells mouse, rat and squirrel apart by ear.

Still unsure? Seal two or three droppings in a zip bag and call Extermination BETA at 438-253-3000. The first inspection is free, and the technician identifies the species on site, in Brossard, Longueuil and across the South Shore. You can also reach us through the contact page.

Why does the mouse versus rat distinction change the treatment?

A mouse lives indoors: nest in a wall, a cabinet or the attic, entry point the width of a pencil. The treatment happens inside the house, and then the small openings get sealed.

A rat almost always lives outside and comes in to feed. Its burrow has to be found, along the foundation or near a sewer line, and its entry point is larger: a drain pipe, the gap under a garage door, a widened foundation crack. The structural risk is bigger, because a rat chews framing lumber, wire insulation and plastic plumbing. And rat bait stations are larger, locked, anchored to the ground and placed outdoors along the runways.

That is why species identification is the first step of Extermination BETA's rodent control service. A single rat inside a house almost always means there are more outside.

How do you clean up rodent droppings safely?

Two rules: never sweep dry and never vacuum, even with a HEPA filter. Both put contaminated dust into the air.

1. Air the room out for 20 to 30 minutes if it is enclosed, and put on gloves.
2. Spray the droppings and the surface around them with a household disinfectant or a mix of one part bleach to ten parts water. Wait five minutes.
3. Pick everything up with paper towel, put it in a bag, seal that inside a second bag and throw it in the garbage.
4. Wipe the surface a second time, take off the gloves and wash your hands with soap.

Hantavirus is carried by the deer mouse, a species of woodlots and fields, not by the house mouse found in homes, and human cases in Quebec are very rare. The realistic risks in your house are salmonella and the other bacteria rodents leave on food and counters, and the allergens in their urine, which stay in household dust and make asthma worse in children. Any opened food in a visited cabinet goes in the garbage.

What should you do next, and when should you call an exterminator?

Three things in the next 24 hours: put all food in hard containers with lids, mark the spots where you found signs with a bit of tape, and do not plug the holes yet. Sealing with rodents inside pushes them to chew through somewhere else or die in a wall.

For a few mouse droppings in a single spot, one or two well-placed snap traps may be enough. Call a professional as soon as any of these applies:

• the droppings are rat droppings, even one, or you found a burrow outside;
• there are fresh droppings in more than one room or on more than one floor;
• you rent and the problem affects several units (notify the landlord in writing as well).

On cost, in Quebec you generally pay 250 $ to 700 $ for a mouse treatment with inspection and follow-up, and often 400 $ to 1,000 $ for a rat problem, which means treating outside and inside. Sealing the entry points is extra, 200 $ to 1,000 $ depending on the number of openings. Every house is different, so call for an exact quote.

Frequently asked questions

Can mouse droppings be confused with bat droppings?

Yes, especially in an attic. Bat droppings crumble into a shiny powder when crushed (they are insect remains), while mouse droppings stay hard or pasty.

Are there rats in Brossard and Longueuil?

Yes, but far fewer than mice. In South Shore residential neighbourhoods, the large majority of rodent calls turn out to be mice. Rats concentrate near sewers, restaurants and open compost bins.

Do you need a mask to clean up?

For a few droppings in a cabinet, gloves and the wet method are enough. For an attic or a cottage closed up for a long time with heavy droppings, add a well-fitted N95 mask and air the space out first, or leave the cleanup to a professional.

Mouse or rat, the answer is in the size

Pointed rice grain, 3 to 6 mm: mouse. Rounded capsule, 15 to 20 mm: rat. Fresh and glossy: the problem is active.

Extermination BETA is based in Brossard and serves Longueuil, Saint-Hubert, Saint-Lambert, Greenfield Park, La Prairie, Chambly, Montreal and Greater Montreal, with same-day response and a real 24/7 emergency line. Our technicians are certified and hold the Quebec CD pesticide permit. Call 438-253-3000 or reach us through the contact page. The first inspection is free, and you get 15 percent off your first service.