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Describe how pests can be a source of contamination.

Pests (rodents and cockroaches) can be a source of pathogenic and spoilage microorganisms, toxins, and allergens. This is one reason that they need to be eliminated from the food processing/food preparation environment.

The hazards associated with pests enter food through one of two ways: (1) direct incorporation of the filth (that is the bodies or parts of the bodies of insects, mites, rodents, birds and other animals) into food or (2) the contamination of food or food-contact surfaces by the metabolic products released by those pests and the microorganisms that they carry.  Table 1 lists a selection of microbial pathogens and known sources of them.

Table 1.  Examples of microbial pathogens and their host.

Pathogen                               Host

Bacillus cereus                        Ants

Campylobacter jejuni              Flies   

Clostridium perfringens           Ants and roaches

Entamoeba histolytica             Flies, roaches, and rats

Escherichia coli                       Ants and flies

Salmonella spp.                       Ants, flies, roaches, and rats

Shigella spp.                           Ants and flies

Staphylococcus aureus             Ants, flies, and roaches

Streptococcus pyogenes           Ants

Here are some additional facts about rodents and cockroaches that might be of interest.


Rodents have one thing in common, strong well developed front teeth called incisors. These four teeth grow six inches in length a year and the rodent must gnaw and chew to wear them down. The enamel on a rodent’s incisors extremely hard and is often compared to the hardness of a steel blade of a pocketknife. When rodents gnaw and chew, they exert a force of about 24,0000 pounds per square inch.

Because of their strong jaws and teeth, rodents can successfully gnaw on a variety of materials including wood, plaster, plastic, aluminum, lead pipe, cinder blocks, porous concrete, soft rubber, cardboard, paper, and cloth materials. They gnaw and chew to gain access to food processing facility, warehouse, retail food operation, restaurant, or a home. Rodents also will gnaw and chew to reach a source of food.

Here are a few of the physical traits of a Norway rat. They can:

  • Jump vertically about 3 feet from a flat surface
  • Jump horizontally about 4 feet on a flat surface
  • Drop 50 feet without serious injury
  • Climb horizontal and vertical wires
  • Climb brick or other rough exterior walls that provide footholds
  • Gain entry to buildings through an opening larger than ½ square inch
  • Burrow vertically into soil to a depth of 4 feet
  • Swim as far as 1/2 mile in open water, tread water for 3 days, dive through water plumbing traps, and travel in sewer lines, even against hard water currents
  • Climb vines, shrubs, trees, and can travel along telephone or power lines.
  • Climb inside vertical pipes (1-1/2 to 4 inches in diameter)
  • Climb outside vertical pipes up to 3 inches I diameter; and
  • Climb the outside of any size vertical pipe that is within 3 inches of a wall or other support.

House mice are just as hearty. They can:

  • Vertically jump 12 inches
  • Run up almost any vertical rough-surface material that provides a foothold.
  • Run along horizontally suspended insulated wires, cables, and rope
  • Pass through openings only slightly larger than 1/4-inch in diameter
  • Move, hanging upside down from 1/4-inch hardware cloth
  • Swim when necessary
  • Walk or run along narrow ledges
  • Jump from a height of eight feet without injury
  • Survive subfreezing temperatures given ample food and nesting material

Rats are steady eaters, they settle down and eat large amounts of food at one time.  If food is located in open areas or the amount of food is too large to be easily eaten, then rats will drag it to a protected area before eating it.  Rats are often known to store food for later consumption.  Rats also require water every day and rely heavily on finding a source of free water.

Mice are nibblers, eating small amounts of food throughout the day.  They require very little water and can usually obtain sufficient water from their food.  They can survive long periods of time without it.  Mice particularly like to eat at dusk and just before dawn.  Between these times, they eat more sporadically.

Rodents, both rats and mice, become very familiar with their environment.  Rats and mice have poor vision and rely on their senses of smell, taste, touch, and hearing.  They rely on these senses to learn about their environment, locate food, and recognize potential mates.  Rodents have very sensitive whiskers and specialized hairs on their bodies called guard hairs.  They keep these whiskers and guard hairs in contact with walls and other objects as they move through an establishment.  In this way, the rodent "memorizes" every nook and cranny into which they can escape in times of danger.

Rats are very cautious about new objects and investigate them very carefully.  They may detour through a previously well traveled area to avoid a trap or new food.  After several days they become more comfortable with the object and begin to explore it.  This has allowed rats to survive many environments.  In contrast, mice are very inquisitive.  Rodents that live in a constantly changing environment, such as in a garbage dumpster, are less afraid of new objects than rodents that live in an environment where change rarely occurs.

A rat sheds about 500,000 to 1 million hairs in one year.  They frequently groom themselvse and ingest hair in this process.  More than 300 hair fragments are present in each rodent dropping.  These droppings are usually found in well traveled areas and also in large amounts in protected areas.  The hair shed from the body and in crushed droppings can be carried by air currents to food products in the food processing/food preparation environment.  A rat dribbles about one pint of urine in a month and produces about 25,000 droppings each year.


Although there are about 55 species of cockroaches found in the U.S., four species commonly cause problems in the food industry.  These species of cockroaches are:

  • American cockroach
  • German cockroach
  • Brown-banded cockroach
  • Oriental cockroach

American cockroach

The adults are reddish-brown to dark brow and are 1-1/2 to 2 inches long.  They are among the largest cockroaches.  The wings are fully developed in both sexes and reportedly fly or glide.  They can live for 2 to 2-1/2 years  American cockroaches are also good swimmers.  

Their egg case is about 3/8 inch long and is reddish brown or black.  The female cockroach deposits the egg case that contains about 16 eggs.  They hatch 45 days later and the nymph period lasts 160 days.  During the adult life-span, a female will deposit about 50 egg cases and so can produce up to 800 offspring.

American cockroaches prefer to live in basements and furnace rooms.  They typically live in damp basements and sewers and can also be found around pipes and plumbing fixtures. They may also be found living outdoors during hot weather.

German cockroaches

German cockroaches are the most active and the most common of all cockroaches.  They are usually light brown but can be very dark in color.  Adults are 1/2 inch to 5/8 inch long and are more slender than other cockroaches.  They have two dark streaks or stripes running lengthwise down their back.  Their wings are well developed and folded over  giving them a pointed appearance at the rear end.  They rarely fly.  These cockroaches do not move far from their resting place.  

Their egg case is yellowish or red-brown in color. The female always carries the capsule for about one month until it is ready to be hatched.  It usually contains about 30 to 48 eggs -- more than other cockroaches.  The young mature in about 36 days.  Adults usually live more than 200 days and three or more generations can be produced in one year.

German cockroaches are often found in kitchens and cooking areas because they like heat and moisture.  They live around sinks, water pipes, cupboards, in stoves, under refrigerators, water fountains, and other appliances.

Brown-banded Cockroach 

The brown-banded cockroach looks similar to the German cockroach but is slightly smaller and does not have the two dark stripes.  The adults measure between 3/8 to 1/2 inch long and are dark brown to a pale golden color.  These cockroaches have two brownish-yellow bands that traverse ethe back. The male has fully developed wings and is lighter in color than the female, whose wings are sort and non-functional.

Their egg case is yellowish or red-brown and the female deposits and attaches it in secure places.  Places include furniture, especially the undersides of shelves, the bottoms of drawers, tables andsinks.  There are about 18 eggs in each case and after hatching they mature to adults in 54 days.  The adult life span is about 200 days and there may be two generations produced each year.

The brown-banded cockroach prefers to live in high locations in heated rooms and is often found in cupboards, closets, storage rooms, desks, inside books, book bindings, telephones, and other electronic equipment.  They generally are found in large groups.

Oriental Cockroaches  

The Oriental cockroach is often referred to as one of the filthiest cockroaches.  It is dark brown to shiny black and is 1 to 1-1/4 inch in length.  The male has fully developed, short wings while the female has underdeveloped wings.  The lifecycle of the Oriental roach is similar wto the American cockroach and they are also good swimmers.

Their egg case is dark-brown to nearly black in color and usually contains 16 eggs.  The female carries the egg case for 12 hours to 5 days before deositing it in some protected area. The young mature in about 128 days.  The average adult lives about one year.

The Oriental cockroach is found in cool, damp areas, such as basements, sewers, and crawl spaces.  They live in sewers and sometimes enter a building through sewer drains.  They are also found around toilets andsinks where they are seeking sources of water. In the southern U.S., they can be found living outdoors during the warmer months.


Gorham, J.R.  1989.  HACCP and Filth in Food.  Journal of Environmental Health.  52(2):84-86

Gravani, R.B.  1985.  Food Science Facts for the Sanitarian.  Food Deterioration and Spoilage by Rodents.  Dairy and Food Sanitation.  June 216-217.

Gravani, R.B.  1986.  Food Science Facts for the Sanitarian:  Cockroaches.  Dairy and Food Sanitation.  August 344-345

Waldvogel, M.  2005.  Department of Entomology, NC State University.  Personal communication.