Pest Profile: Peridomestic Cockroaches

Features - PCT News

A guide to finding and treating outdoor harborage sites.

July 20, 2020

In the pest control business, we refer to cockroaches that live their entire lives inside homes or buildings as domestic cockroaches. The German cockroach is a prime example. Those that live both inside and outside or that move in only occasionally are called peridomestic cockroaches. The main peridomestic species are the American cockroach, oriental cockroach, smokybrown cockroach, Australian cockroach and various wood cockroaches. Peridomestic cockroaches often move indoors when the weather outside becomes too hot, wet, dry or cold, or when the population gets so large that the outside harborage can no longer contain them.

Some peridomestic species, like the Pennsylvania wood cockroach, don’t survive well inside and will die quickly. Others though, like American and oriental cockroaches, can survive and breed successfully indoors if they can find an area with enough moisture.

When peridomestic cockroaches become a problem inside, pest management professionals should check for outside sources of the infestation. Unless they can find and eliminate outside harborage sites and pest-proof openings, more cockroaches will find their way inside. They often can find these roaches hiding during the day in cracks and crevices on the building. The best time to inspect is just after sunset when the cockroaches become active. To successfully address peridomestic cockroach problems in an account, consider the following inspection tips:

Check the building exterior. Inspect cracks and crevices on outside walls. Look under siding and check weep holes in brick. Check openings around pipes, wire and cables where they enter the building. Inspect around garbage cans and Dumpster areas.

Check landscaping. Peridomestic cockroaches like moist and shady areas under trees and shrubs that have lots of leaf litter or mulch. Also, check rotting stumps or logs on the ground, wood piles and tree holes. Inspect compost or debris piles. Check planters and pots near the foundation of the building. (In indoor malls and building lobbies, check the planter beds.) Some species live in palm trees, palmettos or under the loose bark of other trees. Stone fences are another common harborage site for peridomestic cockroaches.

Check sewers (see related story on page 94). The American cockroach, in particular, often lives and breeds in sewers and can invade buildings directly from the sewer system. Check sewer vaults (with the help of the local sewer authority) and unused floor drains. Make sure that there is water in floor drains.

Check beneath the building. Crawlspaces, subbasements and storage voids can serve as harborage sites for peridomestic cockroaches. Also, it’s always a good practice to look under decks.

Check above, too. These cockroaches also can be found under roof overhangs and in roof gutters where they live and feed on collected leaves and debris. Check damaged soffits.


Controlling Cockroaches in Sewers
American cockroaches are one of the largest pest cockroaches and they also have the longest life cycle. There is only one generation produced each year. It takes the nymphs more than a year to become adults, but each American cockroach can live for more than two years.

Unlike the German cockroach which reproduces year round, there is a certain seasonality to the American cockroach’s reproductive cycle. Females deposit their egg case — containing 13 to 18 eggs — at the same time of year, usually in April and May. Nymphs hatch from these cases in early June. This means that American cockroach populations are at their highest in late summer and fall because both older adults and new nymphs are present. In the fall, the new crop of American cockroach nymphs often migrate, looking for food and overwintering sites.

American cockroaches are the most common cockroach infesting sewers and storm drains. When the nymphs leave these sites, they often end up in buildings. American cockroaches are usually found on the lower floors of a building in warm, dark, moist areas like boiler rooms, steam tunnels, garbage rooms, storage areas, basements and greenhouses. They’re generally more common in commercial accounts than in homes.

One of the ways American cockroaches get into buildings is through floor drains. If the trap becomes dry, the roaches will travel up through the sewer pipes. Your customers should flush the drain every week or two to recharge the trap. One way to keep floor drains from drying out is to add about a tablespoon of mineral oil to the water inside the floor drain. The oil floats on top of the water and keeps it from evaporating.

American cockroaches also end up inside a building when a primary sewer line backs up, flushing roaches into businesses or homes. An unnoticed break in a sewer pipe can continuously feed cockroaches into a building. Look for little-used drains, dried-up traps or sump pumps. Ask about any drains that might have been covered by new flooring or renovations without first being plugged.
Eliminating the nymphs at the appropriate time is the best way to prevent problems in the coming year. Action should be taken before the weather turns cold because at that time the cockroaches will find hiding places, will not move around much and will not feed, and will be much more difficult to control. Bait, both outdoors and indoors, is a good choice for control of these roaches in the fall because they are competing for food and will feed on almost anything. Also, apply a perimeter insecticide treatment around the structure, especially on the sides closest to the problem sewers. Thick ground cover around the perimeter of a building provides hiding places for American cockroaches and may need to be removed or trimmed to make control easier. Use a residual insecticide in indoor infested sites. Crawlspaces also may be infested and may require treatment.

In some instances, American cockroach problems can become so bad that populations in sewers will need to be controlled, but this can be a complicated “political” issue because the sewers are generally owned by a sewer authority and not by the property owner, so only the sewer authority has the legal right (and responsibility) to control cockroaches in the sewers. Sewer authorities also will be concerned about the effect of pesticides on their treatment plants and rivers or lakes downstream. Remember, do not enter a manhole or sewer for inspection or treatment unless you have been specially trained in a “Confined Spaces” program and have the proper safety equipment and then only with a properly signed entry permit.

While the American cockroach is the primary roach in sewers, in some parts of the country other roaches occupy this space. In the Southeast, the smokybrown cockroach is often found in sewers. In the West and Southwest, the oriental cockroach is a sewer inhabitant. The Pennsylvania wood roach is also found in sewers. Therefore, proper identification is essential before embarking on a treatment program. — Larry Pinto


CONTROL RECOMMENDATIONS. A number of Integrated Pest Management techniques are useful when developing a treatment strategy for peridomestic cockroaches. The key to successful control is to treat and seal harborage sites. Consider the following six-step program:

  • When cockroaches are found on the exterior, treat the cracks and crevices where they are hiding with a residual insecticide. Use liquid insecticides or granular insecticides in infested sites around the foundation, especially around windows, doors and other entry points. Treat infested voids with a liquid residual or dust.
  • Make sure the harborage cracks and crevices are then caulked or sealed. Seal openings around windows, doors, vents, pipes and electrical conduits.
  • Install door sweeps, thresholds and weather seals on doors, especially garage doors.
  • Have your customer reduce outside lighting and/or use yellow bulbs instead.
  • Have your customers move stacks of firewood, lumber, stones, etc., away from the foundation, clean gutters and avoid heavy mulching around the foundation. Dead tree stumps should be removed. Debris piles that can’t be moved can be treated with granular bait.
  • Applying a regular perimeter barrier treatment can keep peridomestic cockroaches from moving into the building.

Editor’s note: This article was adapted from Techletter, a biweekly publication from Pinto & Associates, Mechanicsville, Md. To subscribe, visit, or call 301/884-3020.