Myths about Rodents

Few pests generate as many persistent myths as do pest rodents and their management. Who hasn’t heard stories about “rats as big as cats,” and how some rodenticides supposedly make rodents go outside to drink, or perhaps allegedly mummify them? Here are some of my favorite myths:

MYTH: SEWER RATS ARE DIFFERENT FROM WHARF RATS.

FACT: The common commensal rat goes by many nicknames, such as house, wharf, barn, sewer or brown rat. But the correct common name for Rattus norvegicus is the Norway rat. The name supposedly is derived from the fact that the first named specimens were from Norway. Actually, these animals originated in central Asia and spread throughout the world by exploration, commerce and settlement.

The other common commensal pest rat in the United States and many other countries is the roof rat, R. rattus. It’s also called the black, plague or ship rat. This rat is smaller than the Norway rat and is found in warmer areas, such as in California, Texas and Florida.

Cotton rats (Sigmodon spp.) are between rats and mice in size. This native species can be especially common around homes in Southeastern and South-Central United States.

The wood rat or pack rat, Neotoma spp., can be common around homes in the Southwestern states. Many native rodents might invade structures, such as taking insulation from crawlspaces for nesting material.

MYTH: RATS CAN GET AS BIG AS CATS.

FACT: The common wild Norway rat rarely reaches 1 pound. A few examples approaching 2 pounds have been recorded in captivity, but these rats become older and heavier than would likely occur in the wild.

A big Norway rat has a body about 8 inches long, with a tail nearly as long.

Some so-called “rat” sightings in rural areas or along rivers and streams may have been other animals, such as muskrats.

MYTH: THE MICE THAT PEOPLE COMPLAIN ABOUT ARE ALL THE SAME SPECIES.

FACT: The common house mouse, Mus musculus, is present throughout the United States and is the most common commensal mouse pest to be found in and around structures.

But don’t assume the “mouse” your customer is reporting is necessarily a house mouse. Native rodents such as deer mice and voles also can be seen in and around homes. Shrews also can be common and are not even rodents, but insectivores.

Most rodenticides are only labeled for control of Norway rats, roof rats and house mice. Don’t create an off-label product use situation by failure to identify the rodent species before designing your control efforts.

MYTH: RATS AND MICE ARE NOCTURNAL (ONLY ACTIVE AT NIGHT).

FACT: Rats and mice are more active when there is less danger about, which in many cases is at night. But they can dart about during daylight hours as well to secure food and shelter, especially if they have learned there are routes they can take and areas they can go where they will not be challenged. In some environments, such as nightclubs and theaters, rodents may take advantage of the fact that there is less human activity during the day.

Also, consider that rats and mice live in social groups where dominant animals may defend the best shelter, food areas and potential mates. Less-dominant individuals might be forced to be active at more-dangerous times, such as during the day.

Regardless of the time, their eyes and ears are always alert to the slightest sounds or movements.

MYTH: IF YOU SEE RATS OR MICE IN THE DAYTIME, THERE MUST BE A LARGE POPULATION AROUND.

FACT: Individual rats and mice sleep only for short periods and might move about at any time of the day or night. They are more visible during the daytime, and so even small populations may give themselves away by sightings when people are up or businesses are open.

Rats and mice normally will move and forage about in the open much more extensively at night, but sightings are not a good indicator of how many rats or mice are living nearby.

A better indication is the amount of signs in the area, such as burrows, droppings and damage.

MYTH: RATS AND MICE AVOID WATER.

FACT: The Norway rat is an excellent swimmer and can live along streams and rivers. It can catch crayfish, frogs and other aquatic animals to supplement their food. Rats also can survive being carried long distances in floods or on river currents. They will cross ditches and swim drains and stretches of sewer flow to get where they are going. Even mice will swim, and can withstand immersion in water for many hours.

MYTH: RATS AND MICE ONLY BREED AND MOVE INDOORS IN THE FALL.

FACT: Rats and mice can breed year-round when there are adequate food, shelter and warm-temperature opportunities. Rats and mice cannot hibernate, and will spend more time inside burrows or structures to stay warm during cold weather, but still can explore their environments, looking for food and shelter. Invasions of buildings might be more noticed in the fall, particularly in northern areas after frost, when ground cover is reduced and crop fields have been cut.

MYTH: RATS TRAVEL IN “PACKS.”

FACT: Rats live in social groups (colonies) where they establish a “pecking order” of dominance. Rats recognize their own colony members and their place in that society, but do not move or behave in any coordinated or cooperative fashion.

Rats move individually along established routes, although one rat might be seen to quickly follow another. Usually, the largest male rat is the top rat, or alpha male, which will defend his choice of territory, food sites and mates, and might chase subordinate males.

Rats have limited movements in areas where they are established, traveling mostly for nearby food and shelter.

MYTH: THERE IS ONE RAT PER PERSON LIVING IN MANY OF OUR CITIES.

FACT: This is a sound bite that sounds good to politicians or those cautioning about rats, but it has no basis in fact. Rat populations change according to their ability to survive in areas and the amount of food and shelter available.

The one-rat-per-person claim first appeared in a British publication from 1909 referring to rats in the English countryside. An educated guess was made that there was an average of one rat per acre. Coincidentally at the time, there were both 40 million acres of cropland and 40 million people in the country, so the one-rat-per-person figure was born.

Nobody has done the actual research in today’s U.S. cities, although officials in New York and elsewhere have again used the “one rat per person” statement in recent media reports. The only actual rat counts in New York were done in the 1940s, when experienced trappers concluded there was about one rat per 36 people in the area trapped. It is a fact that there are a lot of rats living in most cities, but their distribution is uneven and whether their numbers ever equal the human population is unknown.

MYTH: THERE ARE FEWER RATS AROUND TODAY THAN THERE USED TO BE.

FACT: There are probably as many rats in most cities and towns as there have been for decades. It is true that rat and mouse populations took a downturn when automobiles in the city, and tractors on the farm replaced horses. Since the 1950s, hundreds of millions of dollars have been spent in organized campaigns to control rats in many cities and towns.

We know how to limit rat problems, but time, money and energy are required. As cities age, some buildings, streets and sewers fall into disrepair. With current city budget constraints and the lack of a viable customer base for pest management professionals (PMPs) in many inner-city areas, organized and sustained rodent management efforts can be limited. Under the right circumstances (such as a garbage strike), rat populations can reach problem levels in a few months, and every individual needs to take steps to protect his own property.

MYTH: HAVING RATS AND MICE MEANS POOR SANITATION AND RUN-DOWN BUILDINGS.

FACT: Just about anyone can find themselves with a rat or a mouse problem. Rats can move into areas along streams, through sewers, or when displaced by construction. They can explore even well-maintained properties and invade buildings if they find access to the inside.

Besides garbage, rodent populations can be maintained by food sources like pet food, bird seed, fruit trees and gardens. Harborage can be provided by thick landscaping, mulch piles and accessible sheds or garages with clutter. Crawlspaces and under-deck areas can conceal a new population that grows unnoticed until the damage and signs become apparent.

MYTH: RATS AND MICE ARE SHY ANIMALS AND ARE NOT LIKELY TO ACT AGGRESSIVELY OR BITE PEOPLE.

FACT: Rats and mice have survived for thousands of years living with people by being very cautious. Like most animals, however, they can act defensively and can be dangerous when cornered.

Rats can leap or move toward people, and will readily bite when attacked or handled. Their bite can easily penetrate flesh and cause deep puncture wounds that may strike bone or cut nerves, bringing infection and injury. More than 10,000 people are bitten by wild rodents every year in the United States.

In my next column, I’ll offer 12 more rodent myths — and the true information behind them.

You can reach Kaukeinen, an industry veteran with more than 30 years of experience, at 302-521-4637, or e-mail dkaukeinen@comcast.net.