Rat biology

Get to know your furry, uninvited guests.

What rat is that?
Why are there so many?

Rapid Reproduction

A female rat will produce between 3-6 litters with 5-12 pups per litter during her year-long lifetime.
Rats aren’t monogamous—male rats continue to breed with any and every eligible bachelorette.
Rat gestation periods are incredibly short, averaging only 3 weeks from beginning to birth.
In fact, it's this rapid reproduction rate that led to the creation of ContraPest®.

Getting close enough to identify what kind of rat infests your property isn’t an appealing thought. However, distinguishing the common kinds of rats can be helpful when it comes to getting rid of them.

The majority of homeowners across the United States will encounter a variety of common rats.

Norway Rats
Roof Rats

Norway rats

The Norway rat (Rattus norvegicus) is known by many alternate names: the sewer rat, brown rat, water rat, wharf rat, and gray rat are a few examples. This rat is considered common across the United States. Norway rats will typically nest in the ground, in wall cavities, or under discarded materials in your yard or garage.

How do I identify a Norway rat?

  • Blunt nose, small ears, and small eyes
  • Brown fur lightens toward the underside
  • Tail and ears are hairless and covered in scales
  • Tail is short compared to body
  • Larger rats, up to 18 inches long. Weighs 12-16 ounces (or weights up to 1lb)

What do Norway rats eat?

Norway rats eat a variety of foods but prefer proteins and carbohydrates. Food items from household garbage provide these rats with a balanced diet. They will eat meats, fish, cereal grains, livestock feed, and fresh fruits. They will also kill and eat various small reptiles, mammals, birds, and insects.

Norway rats need an abundant supply of water for survival (roughly 10% of their body weight every day). If infesting the inside of your home, they will seek out water from toilets, sinks, and even condensation collecting on utility pipes. Outdoors, they will search for areas where water collects, like rain puddles.

Roof rats

Roof rats (Rattus rattus) are smaller in size and tend to be more slender compared to Norway rats. Roof rats tend to have longer tails that reach up to and over their heads. These rats are also called gray-bellied rats, white-bellied rats, black rats, and ship rats.

How do I identify a roof rat?

Often mistaken for common house mice, roof rats have pointed noses and large ears. However, what sets roof rats apart from mice is their proportionately large heads and feet compared to their bodies.

  • Large ears and eyes, pointed nose

  • Black or dark-brown fur, can be light or dark on underside

  • Tail is longer than body, can be 7 to 10 inches in length

  • Thinner rat, up to 8 inches long (not including tail), and weighs 5-12 ounces

  • Smaller than Norways and juvenile roof rats can be mistaken as mice

What do roof rats eat?

Roof rats will eat meat and grain, but their coastal roots drive them to prefer fresh fruits, seeds, and nuts. They will also eat snails, slugs, and insects. Overall, roof rats eat smaller portions of food compared to Norway rats.

Roof rats prefer to live above ground in shrubs, trees, or attics. They also love to eat in multiple locations. Knowing where roof rats live and eat can help when outfitting your integrated pest management program.

1 + 1 = 15,000

That math might seem off, but the numbers don’t lie –leave just two breeding rats behind and they can be responsible for the birth of up to 15,000 descendants in just over one year.