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UC Cooperative Extension Ventura County
669 County Square Dr. Suite 100
Ventura CA 93003
Phone: 805.645.1451
Fax: 805.645.1474

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Rats

 
Two types of rats are common invaders of residences. The Norway rat and the roof rat. The Norway rat is a larger animal than the roof rat. Its eyes and ears are small, and the tail is shorter than the combined head and body length. The roof rat is slender and agile, and the tail is longer than the head and body length. This rat may be mistaken for a mouse, especially the adolescent rats which have not reached maturity. The roof rat is the more common species at present on the Central Coast and appears to be the primary cause of current local problems. The comments to follow will concentrate on roof rats.
 
Roof rats are quick to take advantage of human habitation. They establish nests in Italian cypress, Algerian ivy, bougainvillea, oleander, palm trees, yucca, any heavy, dense shrubbery, wood and lumber piles, storage boxes, tool sheds, and houses. The roof rat prefers to feed on such things as oranges, avocadoes, other ripe fruit, walnuts, pet food, snails, grass and bird seed. The signs of rat activity are: (1) Partially eaten fruit. They tend to gnaw a hole into the fruit three-quarters ( + ) of an inch wide and three-quarters to an inch deep, rather than feeding in general over the surface of the fruit. (2) Snail shells on top of fences and high in bushes is another sign. (3) Signs of gnawing on plastic, wood or rubber material. (4) Fecal pellets (rat droppings) scattered randomly in the areas of rat activity. These pellets are dark to black, usually spindle-shaped and about half an inch long. And finally (5) visual sightings of rats running between bushes, along fences, in trees, and on utility cables.
 
To reduce and discourage rat activity: (1) Put away dog/cat food at night; (2) clean up trash, weeds, debris around the house and yard; (3) keep wood piles orderly and well stacked (off the ground if possible) to minimize nesting sites; (4) prune trees and shrubs to reduce the density of the plant – again reducing or exposing nesting sites; (5) clean up and discard or bury fallen and unharvested fruit, and (6) check for and plug all potential entry sites to the house, garage, and/or tool shed. A hole as small as a half inch diameter can provide an entry point. Such points may be around water pipes, utility lines, air conditioner or dryer vents, attic louvers, vent pipes, roof overlaps, crawl space vents, chimney openings. Garage and shed doors are notorious for lacking a “tight” fit. Small holes can be plugged with steel wool. The rats will not/cannot gnaw through steel wool. Larger openings should be closed with metal screening fabric as plastic fabric will not deter the rat.
 
Finally, as soon as a rat infestation is noted, control measures should begin. Trapping is the safest and most definite procedure. When you have a dead rat in a trap, you know that individual has been eliminated from the active population. Traps should be set where rat activity is evident (droppings, feeding residues). Attractive baits for traps are peanut butter mixed with oatmeal, bacon, nutmeats, or a piece of apple. Chemical control can be accomplished using rodenticides. Most of these products are anticoagulant formulations. The rat must feed on this bait several times before lethal levels are accumulated in the rat’s blood. The rodent then dies in the attic, under the wood pile, etc. This type of chemical control is best used outside homes as dead rats in the wall space or attic are not good from a disease vector standpoint.
 
One final note – rats and their fleas are capable of transmitting disease. Although cases are rare, the bubonic plague bacterium is still present in the rodent population of California. A case in a person was recently reported from northern California. Human infection occurs when a flea, which has been feeding on a diseased rat, jumps over and feeds on a person. Therefore, dispose of dead bodies quickly and use rubber gloves when handling the traps and dead bodies. Then dispose of the gloves, and wash your hands thoroughly with soap and water.