Norway rats

Norway rats favor ground-level and underground locations with easy access to food sources and water (in contrast to climbing and roof-dwelling species). These burrowing rodents dig extensive underground tunnel systems beneath the surface, complete with multiple chambers and emergency exits.

Common habitats:

• Burrows beneath buildings, concrete slabs, and foundations, where soil is soft enough to dig, and overhead cover provides protection
• Sewers and drainage systems, which offer water, warmth, and a connected network of travel routes
• Basements and crawl spaces, especially those with moisture issues or poor ventilation
• Areas near garbage, compost, or food storage, which provide a reliable and easy food supply
• Railroad embankments and woodpiles, where loose materials create ready-made shelter
• Barns, warehouses, and industrial buildings, particularly those storing grain, animal feed, or other bulk food products

Norway rats are opportunistic omnivores. They need about 110 calories daily and prefer a nutritionally balanced diet when given the choice.

Preferred foods:

• Meat, fish, and pet food, which are high-protein options
• Grains, nuts, and seeds in pantries, bird feeders, and outdoor storagetes
• Fruits and vegetables, including fallen produce in gardens and orchards
• Insects like cockroaches, which supplement their diet when other food is scarce
• Garbage and discarded human food make unsecured bins and dumpsters major attractants

They require ½ to one ounce of water per day when eating dry foods, but need less when eating moist foods.

The Norway rat's life cycle is alarmingly rapid, which explains how quickly infestations can spiral out of control.

Reproductive facts:

• Sexual maturity: Reached at just three months
• Gestation: Only 21 to 23 days
• Litters per year: Three to six, with peak breeding in spring and fall
• Litter size: Typically seven to eight pups, though it can range from two to 14
• Weaning: Pups become independent at three to four weeks

Under ideal conditions, a single female can produce an estimated 79 young per year. Females can mate again within 18 hours after giving birth, contributing to their explosive population growth.

Lifespan:

• Wild rats: Six to 12 months
• Captive rats: Up to two years or longer

Norway rats are primarily nocturnal, becoming active around dusk. They're creatures of habit, using the same pathways repeatedly—which is why you'll see those telltale grease marks along their routes.

Reproductive facts:

• Neophobic: Initially avoid new objects in their environment, which is why bait stations and traps may take several days to become effective
• Excellent learners: Memorize complex burrow and sewer networks, allowing them to navigate quickly between food sources and shelter
• Strong swimmers: Skilled swimmers, which is why they thrive in sewer systems and are known to enter buildings through broken drains or toilet pipes
• Social animals: Live in male-dominated hierarchies based on size, with dominant males controlling access to food and mates
• Cautious eaters: Sample small amounts of new foods before consuming more, a survival strategy that helps them avoid poisoned bait

They can squeeze through openings as small as ½ inch and are skilled climbers, jumpers, and swimmers. Their gnawing ability is formidable—they'll chew through plastic, wood, and even lead pipes.