Roof Rat

Rodent—Roof Rat

Size

Roof rat (black rat, ship rat) adult head+body length is 6-8 in (16-20 cm); tail length is 7-10 in (19-25 cm); weight is about 5-9 ounces, up to 12 ounces.

Characteristics

Soft, smooth fur; pointed muzzle; large eyes; large, almost naked ears which can be pulled over the eyes. Scaly, dark tail is longer than combined head+body length. Adult droppings are up to 1/2 in (12.5 mm) long, and are spindle shaped with pointed ends.

Color

Brown with black mixed in, to gray, to black on top with white; gray or black underside.

Where

Probably from southeast Asia, but now found around the world. In the U.S. Rattus rattus is most common in coastal and southern states, especially near seaports.

Habitat

Outdoors: roof rats nest in high places such as trees, but sometimes in burrows under plants. Indoors: they nest in high places in structures, but sometimes in basements, sewers, or under buildings.

Diet

Roof rats eat almost anything, but they prefer fruit, vegetables, and cereal products. They get their water often from their food. They eat a lot at one time, and will return to that place time after time. If they do not like a food or bait they quickly become shy of it.

Biology

Roof rats mature in 2-5 months, and are adults for 9-12 months. Pregnancy takes 3 weeks. Newborns get hair after 1 week, open eyes after about 2 weeks, are weaned at 3-4 weeks. Female has 4-6 litters per year, with 6-8 young per litter. They have keen hearing, smell, taste and touch (long whiskers), but bad vision, and are color blind. They are good at running, climbing, jumping, even swimming. They are nocturnal and explore a lot, but are cautious and shy away from new objects.

Damage

Roof rats gnaw, eat stored food, and transmit disease by droppings and urine, bites, and the fleas and mites in their fur.

Invasion

An opening larger than 1/2 in (12 mm) allows entry of roof rats into buildings.

Detection

1. Gnaw marks.

2. Droppings.

3. 4-toed front footprint in front of longer 5-toed hindprint.

4. Dark greasy markings from fur rubbing against surfaces.

5. Shallow burrows under plants.

6. Greasy runways along walls and bare soil runways outdoors.

7. Nibbled food.

Control

1. Concentrate control where most droppings are found.

2. Place traps and bait stations along runways, against vertical surfaces.

3. Wire glue boards to rafters and pipes.

4. Rats are cautious. Pre-baiting with nontoxic bait may be needed.

5. Rats are gluttonous. Use sufficient bait for 1, 2 or more meals baits. For roof rats use high-carbohydrate baits, liquid baits if water source can be eliminated. Burrows can be gassed.

6. If you use any baits, gas, or pesticide, be sure they are registered for this species, read entire label first, strictly adhere to all directions, restrictions, precautions.