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Panic at the sight of a mouse may indeed be a comedy staple, but rodent infestations are no laughing matter. Left unchecked, an infestation may result in costly damage to your home or place of business, as well as costs accrued replacing spoiled or devoured foodstuffs. Even worse, wild rodents are a known disease vector, capable of transmitting pathogens harmful to humans and to companion animals both directly, and indirectly via fleas or mites.

While there exist many different species of rodent worldwide, those most likely to pose an infestation risk in York Region are the brown rat, also known as the Norway rat, and the house mouse.


The brown rat is a relatively large rodent, with a body that typically stretches between 15cm and 20cm in length, and bald, scaly-looking tail that is nearly as long. A mature brown rat will weigh upwards of a quarter of a kilogram. They have course fur, and despite their name, can be dark grey in colour as well as brown.

Rats are capable of breeding regardless of season, and a female rat may bear, on average, between three and five litters a year. Litter sizes range from four young up to more than a dozen, with an average litter size of seven or eight. It can take as little as two months for a brown rat to reach sexual maturity, and as a result, even an infestation beginning with only two rats can create a population explosion in short order.

Brown rats are omnivores, and will eat almost anything depending on availability, though they consume grain, nuts, fruits, and meat preferentially. They are difficult to keep out of foodstuffs, as they are capable of gnawing through many common forms of packaging.

Brown rats are nocturnal, and prefer close, dark locations for their nests. Rat nests located inside a building are most likely to be found in the basement or in the attic, where the rats will be comfortable and unlikely to be disturbed by regular traffic.


The house mouse is a small rodent, with a body length of between 5cm and 10cm, and thin, nearly-hairless tails of similar length. An adult mouse weighs in at between 10g and 25g. Wild mice typically range in colour from pale brown to dark greyish-brown, and their fur is quite fine.

Much like rats, mice are capable of breeding regardless of season, and a single female mouse can bear between five and ten litters a year, with an average litter size of between six and nine young. A young mouse can reach sexual maturity at as little as six weeks of age, making the species extremely prolific.

While mice are omnivorous, they eat grain and nuts preferentially, and will often gnaw through packaging to get to cereal, pasta, and other, similar foodstuffs. They are curious enough that any foodstuffs left accessible in an area they frequent will be fair game for sampling.

Mice are most active in the dawn and evening, and will generally hide from bright lights. They prefer warm, secluded locations, often choosing to nest in attics, cupboards, and wall voids. A mouse infestation will often begin in autumn, as the temperatures begin to plummet, causing the mice to seek out the warmer locales and steady source of food offered by human habitation.


Like most rodents, mice and rats habitually gnaw. They prefer wood, and can cause significant damage to framing beams, floorboards, and furniture if left unchecked. They will also gnaw on drywall, and have even been known to chew on electrical wiring, making a rodent infestation a serious fire hazard. Mice take this behaviour even further, widening or creating holes in floorboards in order to have better access to nests they may have built in the wall voids of a building. Both rats and mice will also destroy textiles in order to get material to line their nests.

Rodents infesting the home are happy to help themselves to any food that's left out, or that they can chew their way into. A single mouse can eat several kilograms of food over the course of the year, and a rat will eat several times as much. They will also contaminate food they've been in contact with via a mixture of urine, feces, and bacteria carried on their paws and fur. For safety's sake, any food container a rodent's managed to get into should be disposed of.

Both mice and rats are known disease vectors. They are capable of carrying a number of harmful bacterial and viral strains, and can spread infection via urine and feces, direct contact (either with a live rodent or a dead one), and food and water contamination.  They also frequently carry parasites, such as fleas, ticks, and mites, which can also transmit infection. When handling dead rodents, live trapped rodents, or matter that has been soiled by rodent urine or feces, it is advisable to wear gloves and a face mask, and to wash your hands thoroughly before eating or making any contact with mucous membranes, in order to minimize the risk of disease transmission.

When cornered or frightened, both rats and mice will bite. Their bites can range from painful to damaging, depending on the number, severity, and location of the bite. Rodent bites are also prone to infection, given the bacteria carried in the animals' saliva. If you've been bitten by a mouse or a rat, you're advised to seek medical attention immediately to prevent infection of the wound, or transmission of any illness the rodent might have been carrying.

Signs of Infestation

While spying an uninvited mouse or rat in your home is a sure sign of a rodent infestation, there are other, earlier signs you should look out for.

Rodents will frequently leave visible signs of gnawing on wooden framing, furniture, or cabinets, and even if the gnawing site itself isn't immediately visible, there will often be signs of shavings or sawdust near the site. It's also possible to find visible, nibbled holes where they've helped themselves to boxed or bagged food.

Both mice and rats produce a significant quantity of feces. Mouse droppings are small, only two or three millimetres in length, and resemble grains of rice. Rat droppings are larger, shaped like blunted pellets, and between 1.5cm and 2cm long. Droppings can often be found in pantries, cupboards, and other areas adjacent to food sources. They might also be found along baseboards, atop exposed beams, and near the rodents' nesting sites.

Both mice and rats have oily coats, and will leave smears of oil and dirt on walls and doors, near any opening they might have squeezed through in pursuit of food or safety. The size of these oily smears will indicate the size of the rodent that produced them - mice leave smaller smudges, and rats larger ones. If they're frequenting dusty locations, they may also leave tracks in the dust, visible as both footprints and tail drag marks.

You may also hear frequent rustling and rattling, particularly at night, when rodents are most active. This is particularly true if the rodents have laired in your attic or wall voids, as those areas transmit sound very well.

If you're particularly unlucky, you may be alerted to an infestation when one of the members of the infesting colony dies. Unfortunately, depending on where the mouse or rat was when it passed, it may be necessary to open a wall or pry up part of the floor in order to remove the corpse.

Controlling Infestations

As with the majority of pests, the best method of control is prevention. Make sure to seal off any openings on the exterior of your house, such as vents, gaps in windows, doors, and the foundation of your home, and around openings for cabling, plumbing, and electrical lines. Small holes can be sealed off with steel wool and caulking; larger holes will require metal screens, metal sheeting, or cement to fill.

You can also make your home less attractive to rodents by denying them access to food sources. Keep any open packages of food inside glass, metal, or heavy plastic containers to prevent rodents from gnawing through them. Clean up spills immediately, and make sure not to leave food out overnight - either human food or pet food. Keep any food waste stored inside in rodent-proof containers, and wash both the trash receptacles and the area you store them in regularly.

If an infestation has already taken root, cleaning up likely won't be enough to eliminate the problem. One possible solution comes in the form of mechanical traps. These include glue boards and other live traps, as well as lethal snap traps and electrocution traps. If the infestation is particularly severe, it may also be necessary to employ rodenticides. Poison baits need to be used carefully, as they will also be harmful to pets and children if ingested.

If you believe you have an infestation, it's advisable to contact a pest control professional. Eliminating rodents efficiently requires an understanding both of the individual infestation and of rodent behaviour - a poorly-placed trap may not catch anything at all, and incorrect use of bait may be harmful to non-target species. A properly-trained pest control professional can assess your rodent problem, and devise a solution tailored to your needs and the particulars of your infestation.