Most homeowners prefer to classify rats as dead or alive, or at least relocated far away from their houses and flats. Choosing the right method to kill or trap a rat for making a dwelling rat-free, however, requires a general understanding of the types of rats.
Although there are, depending on which zoologist is doing the counting, from 64 to over 700 species of rats, there are only two species that most of us will ever encounter. These are Rattus rattus, the common black rat, and Rattus norvegicus, the Norwegian or brown rat. The black rat is smaller, prefers a vegetarian diet, and is mostly aerial, preferring to live in roofs and trees. The brown rat is larger, omnivorous, and burrowing, preferring to live in tight spaces under ground. All rats, however, can adjust to extreme conditions when food is in short supply.
Both black and brown rats are commensal organisms. That is, they take advantage of human food supplies and are seldom found very far from human habitations. Hundreds of other species of rats such as pack rats, kangaroo rats, Polynesian swimming rats, and bandicoot rats usually function independently of humans in the wild. That is why they are almost never a problem for homeowners.
By Vergleich_Hausratte_Wanderratte_DE.svg: Sponk (talk), based on a work by Karim-Pierre Maalej translated by: Sponk (Vergleich_Hausratte_Wanderratte_DE.svg) [CC-BY-SA-3.0 (www.creativecommons.org/licenses/by-sa/3.0)
The two species of rats that are dependent on humans for gathering their food, however, inevitably find their way into houses and apartment buildings and require specialized removal techniques. Here is a quick guide for recognizing and dealing with rats of all the different species homeowners are likely to encounter. Or you can go here to find out more about how to get rid of rats.
Black rats (Rattus rattus)
The black rat is a slender rat with hairless ears. It can be covered with black fur, or it can have a brown coat except fine white hair on its belly. Its tail is longer than the rest of its body. Its ears can be pulled over its eyes.
Black rats originated in India, where they were common as long as 3000 years ago. Moving only 200 meters (about 650 feet) or less from one new home to the next, it took them about 1000 years to reach the Middle East and another 1000 years to reach Europe. The advent of seafaring transport, however, later spread them around the world, although the more aggressive Norway rats usually displace them.
Black rats prefer drier and warmer habitats. They thrive in palm trees in desert locations. Most black rats maintain 3 or 4 dens up to 25 meters (80 feet) apart. Young rats are usually forced out of the den to form new colonies. Although black rats can swim up to 500 meters (1600 feet), they dislike water, higher elevations (over 1000 meters/3500 feet), and winter cold. Female black rats usually bear litters of 3 to 6 young after a pregnancy of 21 to 24 days. Breeding depends on the availability of food rather than on a specific point in a menstrual cycle.
Most experts in rat control advise against using brodifacoum (Final Blox, Talon G) to poison black rats, because it can persist in barns and storage sheds and even on the surrounding grounds, killing birds and other small animals, including puppies and even full-grown cats. Diphacinone (diphenidone, Promar, Ramik) is more often used because it breaks down in the environment faster but persists in the rat’s bloodstream longer, a single feeding on poison often resulting in the death of the rat. Diphacinone is also extremely toxic to both pets and people.
Havahart and similar traps usually have to be used over and over again just to keep black rat populations under control. Trap-shy rats avoid the traps and replenish their population in just a few months of reproduction.
Black rats tend to become very selective feeders. Identifying their favorite food is a good way to enhance success with rat trapping. This strategy works as long as the rats have (1) a shortage of their favorite food but (2) are sufficiently well supplied with food that their survival instincts do not kick in. Because of their relatively limited range, black rats are more easily controlled with an electronic rat zapper and ultrasonic devices.
Brown or Norway rats (Rattus norvegicus)
The Norway rat is a large rat, growing up to 400 mm (over a foot) long and weighing up to 450 grams (1 pound). It has brown fur on its back and gray fur on its belly. It has relatively small ears that do not pull down over its eyes. Its tail is shorter than the rest of its body. Female Norway rats are polyestrous, that is, they are in heat when they are not pregnant, and bear litters of 6 to 11 rats after a pregnancy of 21 days. A female rat can become pregnant within the first 90 days of its life.
Norway rats originated in China and reached Europe between 1700 and 1716. They have spread throughout Europe, the United States, Canada, and Mexico, and also Japan, New Zealand, Chile, and certain islands in the Pacific. They prefer damp places and can swim at least 2000 meters (over a mile). An adult Norway rat marks its territory with urine and feces, and may feed over an area as large as 5 hectares (about 15 city blocks).
Norway rats are voracious but discriminating eaters. They attack all kinds of animals smaller than themselves, including kittens, puppies, birds, and reptiles, and they feed on tender young plants. They tend to sample food they can hold between their paws, allowing up to 80% of a piece of food simply to fall to the floor uneaten. This kind of rat will only eat the freshest grain and dry goods, marking the rest of a food supply with urine as part of its territory.
Rat poison often wipes out an entire population of Norway rats, especially when diphacinone is the toxic agent, but newly arriving Norway rats quickly take their place. Using rat traps on an ongoing basis helps keep the population down. Whichever method is used to bring the Norway rat under control, sealing off entryways and exit points is essential for getting rid of rats for good.
A strategy for trapping Norway rats that often works is depriving them of their water supply and placing water in the trap. Adult Norway rats need about 25 ml (1/8 of a cup) of fresh water every day. They will leave their nests to get water. Norway rats also need about 10% grains in their diet, so depriving them of other grain sources and putting grain in the trap—which they cannot remove and share with other rats—also works.
In most of the world, black and brown rats are the most common household pests. Some other species of rats, however, occasionally show up in houses and flats on the periphery of their range.
Polynesian rats (Rattus exulans)
The Polynesian or Pacific swimming rat often shows up shortly after the leis are passed out to new families moving to Hawaii. It is also common in New Zealand. This rat is smaller than either black or brown (Norway) rats and has a completely brown coat of fur. Its tail may be either slightly longer or slightly shorter than the rest of its body and even the largest specimens are just 150 mm (6 inches) from the tip of the nose to the base of the tail and weigh less than 85 grams (3 ounces).
Oddly enough for a creature that has colonized all of the island chains in the Pacific; the Pacific rat is not a good swimmer. It often burrows into the base of trees, and is seldom seen during the day, although it may swarm just before sundown. You are more likely to encounter these rats in your garden than in your home, since they prefer to eat earthworms, beneficial insects, plant seedlings, and baby birds.
The best time to trap or kill Polynesian rats is during the winter, when they do not breed. Polynesian rats have very short life spans and only relatively aged rats will survive until spring. In Hawaii, these rats breed less often during dry weather, so it is best to deal with them just before the rainy season.
The black rat, the brown rat, and the Polynesian rat are the only three invasive species of rats spreading themselves around the world. Other species of rats are more easily trapped and more easily excluded by a combination of blocking entryways and using electronic and sonic repellants.
Looking for more information about types of rats? Visit the Global Invasive Species Database .