Roof rat season is here: 5 steps to keep them out of your home

Figure 11.  This fact sheet is excerpted from SP486: Pests in & around the Southern Home, which is available from the UF/ Extension Bookstore. Http://

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The roof rat (Rattus rattus, a.k.a. Citrus rat, fruit rat, black rat, or gray rat) is an introduced species of rat native lớn southern Asia. It was brought lớn America on the first ships to reach the New World and has spread around the world. This rat is the same species that carried the bubonic plague around the world & is also the reservoir host for murine typhus. Roof rats are the worst rodent pest in the state of Florida và most abundant. The Norway rat (Rattus norvegicus) that is familiar khổng lồ most people is rare in Florida.

Roof rats consume & destroy stored animal và human food, attack fruit crops, and take up residence in attics, soffits, hollow walls, và out-buildings. When they invade buildings they chew through wires (potentially starting fires), gnaw through plastic & lead water pipes, make holes in walls, & cause other structural damage.

The secretive, nocturnal nature of rats means that they often go unnoticed in a neighborhood until dooryard citrus và other fruit starts lớn ripen. They then make their presence known with a vengeance. In citrus, papaya, cantaloupe, và watermelon the characteristic damage is a circular hole about the form size of a quarter or half dollar và the whole fruit hollowed out (Figure 1).


Figure 1.  Roof rat damage to lớn oranges.


As we progress through the citrus season (from September through March), the roof rats that may have been living quietly around your house or grove make themselves known. Hollowed-out fruit is the most common evidence of roof rats.

In apples, peaches, tomatoes, carambolas, bananas, pineapples, and mangos, large sections of fruit are eaten away. They remove whole fruits from blueberries, figs, grapes, strawberries, lichees, Surinam cherry, loquat, và dates, so the damage is less noticeable or birds are blamed for the missing fruit. In Florida, roof rats—along with our native cốt tông rat—destroy or damage a great deal of sugar cane every year.


Adult roof rats are 12–14 inches long (30–36cm) và weigh 5–10oz. (150–250g). The tail of a roof rat is longer than the head and body length: hairless, scaly, và black color. The body is sleek & graceful with prominent ears and eyes (Figure 2). There are three color phases seen in Florida: đen back with a slate gray belly, gray back with lighter gray belly, & brownish gray above with a trắng or cream colored belly.


Figure 2.  Roof rat.


In addition lớn the damage done to fruit, other evidence includes đen banana-shaped droppings about 1/4-1/2 inch long (about 1 cm) and dark smears or rub marks seen along the rat's travel routes (Figure 3).


Figure 3.  Swing marks.


Range and Habitat

The roof rat occurs along the southern Atlantic và Gulf coastal States from Virginia to Texas và throughout Florida. They also occur along the Pacific coast of California, Washington State, and Oregon.

Roof rats are arboreal (tree-living) by nature. They are similar to squirrels in their ability khổng lồ move through trees & along vines and wires. They often use utility lines & tree branches lớn reach food và water và to enter buildings. They prefer nesting above the ground in attics, soffits, piles of debris, hollow trees, skirts of old fronds on palm trees, & in Quaker parrot nests, but will nest in burrows in canal banks and under sidewalks or stacks of materials stored on the ground.


Roof rats are omnivores (plant- & animal-eating) but are very fond of fruit. They feed on most cultivated fruits and eat many native fruits và nuts. They also feed on livestock feed, pet food, bird seed in feeders, và garbage. They contaminate và damage much more than they actually eat. They will chew through lead and plastic pipes khổng lồ reach water. They will travel 150yds. (135m.) from their den khổng lồ reach food or water.


Roof rats reach sexual maturity at 3 to lớn 4 months of age. In Florida, they breed year-round, with peak breeding activity in spring and fall. The litter of 5 to lớn 8 pups are born after a gestation period of 21 khổng lồ 23 days. A female roof rat can have 4 or 5 litters per year.


Control of roof rats is not an easy task. Integrated pest management is needed lớn control these pests. The tools of Integrated Pest Management (IPM) include inspection; cultural control (prevention & habitat management); physical control (trapping và exclusion); biological control (predators); and—if needed—chemical control (rodenticides và repellents).


Because roof rats are such good climbers & swimmers it is hard lớn completely exclude them from your yard, grove, or orchard. Here are some cultural techniques lớn help you reduce damage.

Proper Spacing and Pruning of Fruit Trees

Your fruit trees should be isolated, not touching fences, overhead wires, or the branches of other trees. Roof rats will run along fence stringer boards or tư vấn poles, phone & cable TV wires, & tree branches to reach your fruit tree. Lower branches of the tree should not touch the ground. A low-hanging skirt of drooping branches give the rats additional access routes & provides them with protective cover while feeding. Prune trees so that the ground under them is xuất hiện and visible. This lack of cover makes the rats uncomfortable and more susceptible khổng lồ predators.

Rat guards on the trunks will keep the rats out of trees (Figure 4). Rat guards can be as simple as a piece of sheet metal 18–24 inches wide and as long as the circumference of the tree plus two inches. Use a piece of wire bent like a giant staple to secure the ends of the sheet metal without penetrating the tree. Put the back of the wire against the tree's trunk và insert the two ends of the wire through holes in the sheet metal. Then bend the wire outward lớn hold the ends of the rat guard together. If your tree has a short or forked trunk, then a sheet metal wall, 2 feet tall (60 cm), around the tree will reduce rodent access lớn it. If wires go through the crown of the tree or your tree touches a fence or branches of another tree, then rat guards are useless—the tree must be isolated for rat guards to work. Sanitation is also important. Use or remove all fallen fruit.


Figure 4.  Rat guards on the single trunk fruit tree & around a multi-trunk tree.


If you have more fruit than you can use, contact your local food banks or become involved with community fruit salvage operations.


Trapping rats has many advantages over the use of poisons. It greatly reduces the risk of the poisoned rat finding its way into your home or buildings, dying, and causing an odor problem.

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The tree can also be protected by tying several rat traps around the trunk of the tree with the triggers pointing down. Use expanded trigger rat traps on trees và fences. Be sure lớn tie the traps securely to lớn the trunk before trying to set the traps. The next time a rat tries to lớn climb the tree it will get caught & killed or at least given a good scare. Set rat traps only from dusk to dawn khổng lồ avoid accidentally killing non-target species like squirrels & protected birds, such as wrens, woodpeckers, chickadees, etc. These animals are diurnal (active during the day) while rats are nocturnal (active during the night).

Since rats prefer lớn stay off the ground, they lượt thích to run along the stringer boards of fences và the horizontal tư vấn poles of chain liên kết fences. Traps can be nailed directly to the horizontal stringer board of wooden fences. Place a protective board above the trap lớn discourage birds from accidently getting in the trap (Figure 5). To secure rat traps khổng lồ horizontal poles of chain link fences, put an eye screw on each side of the trap & use several heavy rubber bands to lớn hold the trap lớn the pole (Figure 6) & (Figure 7). As stated before, traps should be mix only from dusk until dawn to avoid killing non-target animals active during the day. Use of live traps will also prevent the accidental killing of birds & squirrels.


Figure 5.  Rat trap secured lớn the stringer board of a wooden fence with a protective cover board to lớn reduce accidental killing of birds and other non-target animals.
Figure 6.  Rat trap secured to the support pipe of a chain link fence.
Figure 7.  Rat trap secured khổng lồ the support pipe of a chain link fence showing the use of eye screws và rubber bands lớn secure the trap without slipping.


Roof rats are nervous & cautious of new objects in their environment, so leave traps in the same location for at least a week before moving them.

Use of Poisons

If poison baits are used outdoors, they must be placed in a tamper-resistant bait station. All rodenticide labels in Florida state that it is illegal khổng lồ place any poison rodenticide baits where they are accessible to children, pets, livestock, or wildlife, unless the bait is contained in a secured, tamper-resistant bait station (Figure 8).


Figure 8.  Tamper proof bait station secured firmly in a fruit tree.


The practice of wiring poison bait blocks to lớn branches of trees is illegal and has caused thousands of cases of accidental poisoning of dogs & wildlife each year. Tamper-resistant bait stations lượt thích those in Figure 6 are not usually found in retail stores. Try pest control companies which may sell them or can refer you khổng lồ another source khổng lồ order them.

Plans for building an effective bait station are included in this fact sheet (Figure 9).


Figure 9.  Inverted T bait station secured khổng lồ a fence stringer board with locking cables.


In Florida, due to our high humidity, parafinized bait blocks or pellets should be used in any outdoor bait stations. Some municipalities và counties have rodent control programs, but most vày not. Tương tác your local đô thị or county government khổng lồ find out if there are programs in your area.

There are no repellents registered specifically for roof rats. Since most wildlife repellents cannot be used on human food plants, their usefulness in rat control on fruit trees is extremely limited.

Biological và Behavioral Control: IPM

Integrated Pest Management, we often rely on biological control agents as a cost-effective way of controlling pests. We have many allies in our war on rats.

Snakes. In Florida, many species of snake help control roof rats. Yellow rat snakes (Figure 10), gray rat snakes, corn or red rat snakes, black racers, king snakes, coachwhips, and indigo snakes all prey on roof rats. Even our venomous rattlesnakes and cottonmouths eat lots of rats.


Figure 10.  Yellow rat snake.


A Cautionary Tale. The importance of snakes in rat control was made clear in the following report: A dog kennel worker took it upon himself lớn eliminate all of the snakes at his place of work. Once the rat snakes had been killed, the roof rat population exploded.

It took two years, hundreds of people-hours, và thousands of dollars to get control of the rats và repair the structural damage the rats had caused. This does not include the hundreds of pounds of dog food the rats ate & contaminated. The economic cost of removing the rats' natural predators was obvious.

Raptors. Hawks và owls, especially barn owls, are very effective at killing roof rats. Keeping the area around fruit trees mở cửa makes hunting easier for birds of prey.

Cats & Dogs? Many people believe that cats & dogs will keep rats out of their yards và fruit trees. But, because roof rats are so arboreal, they are usually able khổng lồ get into attics và fruit trees without ever coming to lớn the ground. Rats quickly learn safe travel routes through yards khổng lồ avoid terrestrial predators. Cats will kill dispersing juvenile rats, but are rarely able khổng lồ handle an adult roof rat within its own territory.

Ultrasonic và Electromagnetic Devices. Many claims are made about ultrasonic and electromagnetic devices' repelling rodents from buildings and yards. There is no evidence that these devices will or can drive rodents from their home range. There is evidence that ultrasonic devices can cause hearing loss in pets, especially dogs.