Old-World or European rats, roof rats (Rattus rattus) and Norway Rats (Rattus norvegicus), have been living in association with human populations for centuries. Once transported into a new geographic area, they generally breed quickly, since they have adapted to living in urban areas.

For information on the Rodent Surveillance Program, visit the Zoonotic Diseases webpage.

Norway Rat

The Norway rat is larger and more aggressive than the roof rat. The Norway rat has a short tail, shorter than the head and body combined, with a blunt nose and small ears. The Norway rat may weigh 12-16 ounces and grow to a total length of 13-18 inches.

The Norway rat thrives in unsanitary conditions, and is an opportunistic scavenger. Norway rats are much more likely to infest structures than are roof rats.

Roof Rat

The Roof rat is smaller than the Norway rat, weighing only 5-10 ounces, with an total length of 10-14 inches. Roof rats have larger ears than Norway rats, and tails longer than their bodies. Roof rats prefer “natural” foods such as seeds, nuts, fruits and vegetables, but will scavenge if necessary.

Both species are nocturnal, foraging at night, and usually stay in or close to burrows during the daytime. Both species are rarely seen during the day, unless the competition for food and habitat is significant. Both require heavy vegetation for burrowing and a reliable source of water.

These species can reproduce quickly, becoming sexually mature in 2-3 months, and are capable 4-6 litters per year, with 4-8 pups per litter. This allows infestations to expand rapidly if they have an adequate habitat.

In the Las Vegas Valley, Norway rat activity has been rare. Roof rats have been documented in the Las Vegas valley since 1990. Initial identifications were made in the south/central part of the valley, and associated with imported palm trees. Reports of roof rats are often associated with areas near washes and/or areas with heavy vegetation and standing water.

Uncontrolled rodent populations can cause significant adverse affects in the community.

• Roof rats can produce large quantities of fecal pellets, urine, and hair, which are capable of soiling and contaminating large areas.
• Nesting, burrowing and gnawing can cause direct property damage.
• Roof rats and their associated parasites can transmit plague, typhus, salmonella, leptospirosis, rat bite fever, and other diseases.

Rodent Control Measures

• Weatherproof your home’s windows and doors (eliminate light from around doors).
  • Seal outer openings, pipe chases and wire entrance gaps with steel wool, aluminum, or wire mesh.
  • Secure pet doors at night.
• Eliminate any unnecessary clutter, material, brush or foliage from your property.
  • Keep bushes trimmed and clean out leaf litter and clutter that collects below bushes.
  • Remove landscaping debris quickly.
  • Stack firewood 12 inches off the ground and keep the area clean.
• Keep trash cans (plastic or metal) covered.
  • Do not put out “food” garbage in plastic bags.
  • Place sealed plastic bags in trash cans.
  • Do not leave pet food outside overnight.
• It is recommended that rodent control be conducted by a commercial pest control company that is licensed by the Nevada Department of Agriculture.
  • After rodent-proofing, glue and snap-type traps are effective in reducing rodent numbers.
  • Do not place traps where they may be accessible to children or pets.
  • Over-the-counter poison baits can also be useful, provided the label directions are followed, but should not be used in households with children or pets, unless under the direction of a licensed pest control company.

Download the Rodents Checklist PDF (222 KB/5 pages) to learn more on how to inspect for rodents on your property.

For more information on rodent pests and control measures, visit the links from our Related Websites page. Information on the Rodent Surveillance Program is available on the Zoonotic Diseases webpage.