This document contains information about the biology and management of the Norway rat. A wide range of management options is listed. From this list, the IPM Practitioner can choose options to develop a unique management plan for each particular customer site.

General Information

Management Objectives for the Pest at the Particular Site

What do you want/need to accomplish at the site in regard to the Norway rat? The answer to this question will vary, depending on the site and the customer. Some examples are:

• Reduce rat complaints in the building and work with occupants to prevent future complaints
• Work with the building manager or homeowner to prevent future rat infestations
• Help client comply with Health Department regulations

 

Norway Rat Identification

• Scientific name is Rattus norvegicus
• Other common names include brown, wharf or sewer rat
• Adults weigh between 3 and 21 ounces
• They are typically brown or black with a shaggy coat
• They have small, thick ears with short hairs and a blunt snout
• They are decent climbers which nest inside in walls and cluttered areas and outside in burrows or unused sewer or storm drains
• Adults are excellent swimmers

 

Why the Norway Rat is Considered a Pest

• Rats contaminate food and eating utensils
• Rats can cause substantial damage to research collections, living collections and exhibits.
• Rats can cause millions of dollars with damage to structures by gnawing on doors, walls, ceilings and floors. They cause fires, explosions, indoor flooding, and damage to computer systems as a result of their gnawing on utility pipes and electrical wiring.
• Rats have the potential to carry a number of harmful diseases
• They can also carry tropical rat mites that can bite humans and cause serious annoyance

 

Special Regulatory Conditions

California Health and Safety Code Sections that relate to rats and cleanliness in food establishments:

114010. “All food shall be prepared, stored, displayed, dispensed, placed, transported, sold, and served as to be protected from dirt, vermin, unnecessary handling, droplet contamination, overhead leakage, or other contamination.”

114030. “A food facility shall at all times be so constructed, equipped, maintained, and operated as to prevent the entrance and harborage of animals, birds, and vermin, including, but not limited to, rodents and insects.”

114040. “The premises of each food facility shall be kept clean and free of litter, rubbish, and vermin.”

114050. “All food facilities and all equipment, utensils, and facilities shall be kept clean, fully operative, and in good repair.”

Biology and Behavior of the Norway rat

To be successful, management strategies must take into consideration the biology and behavior of the pest. Understanding the biology of a pest can reveal weaknesses and vulnerabilities that can be exploited when trying to manage the pest.

General Biology of the Norway Rat

• Adults are polyestrous (multiple breeding cycles). In subtropical climates rats can reproduce year round.
• In cooler climates populations peak in spring and fall.
• The average litter size is between 5 and 12.
• They can have up to 9 litters per year depending on food availability. The Norway rat has an average of 4 litters per year.
• The gestation period is 20-25 days.
• It takes around 30 days for weaning
• The Norway rat takes 75-90 days to reach sexual maturity.
• They have poor eyesight, but an excellent sense of smell, taste, touch and hearing.
• Rats have highly sensitive body hairs and whiskers (called vibrissae) that help them navigate
• Lifespan is generally under 1 year.

 

Feeding Behavior

• Usually search for food between dusk and dark
• Rats feed on all kinds of human and pet food.
• Norway rats prefer foods high in carbohydrates or protein but will eat almost anything including non-food items such as soap.

 

General Behavior

• Rats are mainly nocturnal, but can be seen during the day if colonies are overpopulated.
• They prefer to travel along edges, along pipes or rafters, along the outside or inside of a foundation.
• Rats are generally wary of crossing open spaces that provide no cover. Hedges and other dense vegetation in landscaping or against buildings provide cover for rodent trails.
• Rats are usually extremely wary of new objects in their environment; however this is only a temporary hesitation.
• Rats can fit through openings the size of a dime.
• They also have amazing physical abilities that allow them to climb vertically in pipes, walk horizontally along wires, and jump from a standstill vertically at least 24 inches and horizontally at least 4 feet. They can also drop from heights of 50 feet without injury.
• All rats can swim. The Norway rat in particular is an excellent swimmer, which can swim a half-mile in open water and tread water for up to 3 days. They have also been known to swim up through the water seal of a toilet.
• Rats will gnaw through almost any material with an exposed edge including, wood, chip board, lead pipes, cinder blocks, aluminum, sheet metal and glass.

 

Factors that Favor the Norway Rat

• Poor sanitation provides rats with ample quantities of food to sustain large numbers of rats.
• Improperly stored food and waste allows another food resource for rat populations to flourish on. Pet foods are a common meal for rats and should be stored properly as well.
• Clutter and improper storage practices provide abundant hiding places, nesting sites, and travel routes for rats.
• Dense vegetation and ground cover can act as excellent nests and rat highways.

 

Monitoring and Record Keeping

The purpose of monitoring is to track pest activity in order to catch small problems before they become overwhelming. Monitoring also makes it possible to properly time pest management actions and to evaluate the effectiveness of those actions. Records are kept to document the methods and products used and to record information that can be used to fine-tune pest management methods and plan future actions.

Visual inspection coupled with snap or glue traps are the most effective means of monitoring for the Norway rat.

Tolerance Level

The “tolerance level” is the number of Norway rats that triggers action to control the pest. The tolerance level is site-specific and differs depending on the customer, the location, and other factors. Determining the tolerance levels for a site helps prioritize work that must be done to control the pest.

Management Strategies

Pests need food, water and shelter to survive. Pests also need access to a structure and a way to move around within the structure in order to make them a nuisance inside a building. If even just one of these factors can be reduced (or eliminated), the environment will support lower pests and pests will be less likely to invade our living spaces.

Habitat Modification

To limit availability of food and water

• Store food properly: in the refrigerator, in metal, glass, or heavy plastic containers with tight fitting lids.
• Do not leave food out overnight.
• Store bags of pet food, bird seed, and grass seed in rodent-proof containers, or at the very least, inspect them often for any signs of gnawing.
• Pick up fallen fruit and nuts from trees daily.
• Pick up animal droppings daily.
• Never leave uneaten pet food inside or outdoors for any length of time. You cannot count on dogs or cats to keep rats away.
• Limit areas for eating and storing food and enforce these rules. The fewer designated areas, the easier it will be to limit pests.
• Fix leaky plumbing and eliminate any unnecessary standing water.
• Dispose of all garbage in dumpsters or garbage cans with tight fitting lids that are kept closed.
• Remove all garbage from the building at the end of the day
• Wash all garbage cans that contact food wastes with soap and water at least every 2 weeks.
• Require your refuse company to clean the dumpster or replace it with a clean one frequently.
• Never store extra garbage outside the dumpster or garbage cans, even if it is in cardboard boxes or plastic bags.
• Avoid planting date palms because rats can feed on and nest in these trees.

To limit availability of shelter/harborage

• Seal all openings in a structure that would allow access to the structure.
• Reduce clutter and debris by using proper storage techniques.
• Remove rock and wood piles and construction debris.
• In warehouses and commercial storage areas, store items on pallets 12 inches off the floor in rows 6 feet wide or less, and at least 18 inches from any wall. This creates aisles for inspection and cleaning.
• Trim trees, vines, bushes, grass, and weeds at least 2 feet from all buildings to decrease cover for rodent runways, to prevent hidden access to buildings and to make inspections easier.
• Trim tree and shrub branches 3 to 6 feet away from the building.
• Eliminate dense plantings or break them up with pathways, stretches of lawn, or very low groundcover.
• Avoid large expanses of low groundcover that could allow rats to run for long distances without being seen.
• Eliminate plantings of Algerian ivy (Hedera canariensis) because rats can live in and feed on this ivy. If you cannot eliminate these plantings, work toward that goal. And in the meantime, mow or shear the ivy very close to the ground.

 

Physical Controls

Physical controls employ physical means to remove rats or prevent their access to or movement within a structure.

• To prevent rat entry:
• Trim trees and bushes at least 2 feet from the structure.
• Make general building repairs and seal large and small holes in structures both inside and out. Seal small holes with steel or copper wool and caulk.
• Seal vents with ¼ inch hardware cloth.
• Seal gaps where pipes and wiring enter the structure.
• Weather-strip doors and windows, use metal kick plates or raised metal doorsills to prevent rodent entry.
• Make sure air conditioning units are well sealed, especially those on the roof.
• Repair broken sewer pipes.
• Install threaded caps on drains.
• Use snap traps or glue boards and record their location on your site plan.
• Use as bait the food rats are already eating. For Norway rats use pieces of hot dog, bacon, liver, peanut butter, or nutmeats.
• Move objects around to funnel rats into traps.
• Monitor traps regularly and frequently, and keep bait fresh. Rats avoid old or rancid bait.

 

Chemical Controls

In general, chemical controls should be used as a last resort or in emergency situations. Rodenticides can pose hazards to non target animals, including children and dogs. Poisoned rodents may also die in inaccessible places and cause odor and fly problems. Overuse of many rodenticides has lead to widespread resistance. Exclusion methods are favored over any chemical means.

The IPM Partnership

The PCO-Customer Partnership is Very Important

IPM works best when the customer and Pestec form a partnership to tackle the pest problem. The Norway rat cannot be managed satisfactorily without the cooperation of the customer, especially in the area of sanitation. Pestec will discuss the findings of the initial inspection and any subsequent monitoring sessions with the customer to determine which issues and tasks will be the responsibility of Pestec and which will be the responsibility of the customer.

Education

Information is a powerful tool in IPM. Information can help change people’s behavior, particularly in how they store food and dispose waste. Changing these behaviors is often an invaluable part of managing rats. Building occupants and homeowners can also help in the early detection of pests so that Pestec can be alerted before the problem is severe.

Pestec’s highly trained and knowledgeable staff can provide pest management education or training sessions for facilities managers, risk managers, building occupants, homeowner associations, and others.