Roof rats are native to Asia and Europe, and are an “old world” rat. They were introduced to the Americas when early ships first arrived, hundreds of years ago. A crafty, secretive animal, Rattus rattus had no trouble surviving long journeys on ships.
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Since that time, the “roof rat,” also called the “black rat, fruit rat, ship rat, or house rat,” has spread, and unfortunately, roof rats are now present in large numbers in the Mojave Desert, causing considerable financial loss and headache to those who are unfortunate enough to experience an infestation. In this region, roof rats are normally a grey/brown color, often have a white stomach, (but may be darker) and have a long, nearly hairless or hairless, scaly tail at least as long as the body.
Roof rats will eat just about anything, and need to constantly gnaw on items to keep their teeth (which grow throughout their entire lives) trimmed. Vehicle wiring, wood, vinyl siding, appliance and home insulation, aluminum siding, electrical wiring, paper, and even some types of metal and concrete are no match for a roof rat’s gnawing.
Commercially grown crops, home gardens, livestock and poultry waste, hay, grains, pet food, fruit from trees and vines, trash, leather, tree bark, metal and plastic plumbing (to gain access to water) and even chicken feathers are on a roof rat’s menu. In agricultural areas, they cause significant financial losses due to crop damage.
Roof rats are capable of climbing any rough vertical surface. Bricks, cinder block, and stucco several stories high are scaled with little effort.
In times where little to no food is available, they may cannibalize one another. They cause significant damage or destruction to the interiors of attics and beneath homes, in garages and sheds. Roof rats are highly secretive, nocturnal, very quiet, and are neophobic, meaning they are fearful of new things. Neophobia can make controlling infestations a challenge.
They may nest in trees, cactus and Joshua trees, piles of yard waste, abandoned cars, ivy or similar deep ground cover, in chicken coops, inside bales of hay, the burrows of other animals, attics, thick shrubs, inside of walls, basements, engine compartments, under pallets, and in the rafters of sheds and barns.
Rats will not leave of their own accord. Those that leave are those are forced to, once an area cannot support an increase in population due to frequent breeding, and the cycle continues. Dominant rats have nesting and feeding “rights,” with other rats eating only after dominant rats have left feeding areas. Once they have found food and shelter, they’ll remain and breed constantly, creating an unhealthy mess of nests, droppings and urine. They may nest on one property, yet feed on another.
Roof rats live approximately one year, but sometimes longer. Females live longer than males. A juvenile roof rat reaches breeding age by 12 weeks, and a female roof rat will have 4 to 6 litters per year. Each litter averages 5 to 8 pups.
Rats must be trapped and completely eliminated not only to preserve property and human health (when found in buildings) but to stop the spread of roof rats to new areas. They carry fleas and ticks, and are known to carry and spread murine typhus, leptospirosis, trichinosis, salmonellosis, rat bite fever, and plague via infected fleas and ticks, in nests, etc. Anywhere a rat has been is a potential source of contamination. Dried urine and droppings can cause significant respiratory problems. For more information on diseases, see Wildlife Diseases and Public Health. In agricultural areas, regular control is a necessity.
All areas that roof rats can gain access to must be corrected. This may include not only exclusion techniques on all vulnerable areas of homes and other buildings, but removing trash, junk, and brush piles, strictly controlling both plant and animal compost piles, trimming of tree and shrub branches at least 20 feet away from homes (especially roofs) keeping all livestock feed (including hay) in steel, securely covered containers, examining all bales of hay for evidence of rat infestation prior to purchase, removing all livestock and poultry waste on a daily basis, not leaving pet food or water bowls outdoors, and keeping all trash cans and dumpsters securely covered at all times.
Never handle dead rats, rat nests, or waste with bare hands, or enter areas where rats may be living without appropriate personal protective equipment.
Myth or fact? Rats will avoid areas where soap, peppermint oil, soap flakes, or mothballs are placed.
Myth: Rats eat soap, and ignore mothballs and peppermint oil after a very short time, if at all. Mothballs are toxic, and should not be used in any manner other than what is stated on the label. If any of these methods actually worked, pest control companies worldwide would be using them.