Q. For about the last year, I’ve been finding these very large reddish-brown cockroaches in my basement. Not a lot of them, just a few occasionally, Then I found out that two of my neighbors have the same problem. Do these roaches move from house to house? Are they coming in from outside or what?

A. I think you’re probably talking about the American cockroach, which is the largest roach that gets into buildings. It is also the most common cockroach infesting sewers and storm drains and that could be where your cockroaches are coming from. In the southern U.S., American cockroaches do live outdoors in mulch and vegetation. But in our Northeast, they are not outdoor pests in landscaping but instead seek the heat, moisture, and abundant organic matter in sewer tunnels.

When the roach nymphs leave the sewers, they often end up in homes. American cockroaches are usually found on the lower floors of buildings, in warm, dark, moist areas. They are more common in commercial buildings where they infest boiler rooms, steam tunnels, garbage rooms, storage rooms, and basements. It does occasionally happen that a neighborhood will have a chronic problem with American cockroaches in homes that is traced to the sewer system.

If the cockroaches are coming from the sewers, it probably means that there a high population that is moving out to infest new areas. American cockroach nymphs hatch out in early summer so in late summer/early fall, both old adult cockroaches and new nymphs are present. The nymphs often migrate out of the sewers in the fall, looking for food and places to spend the winter. The roaches can exit to the street through vent holes in manhole covers or can find their way into buildings directly from the sewer system.

One of the ways American cockroaches get into buildings from the sewer is through dry floor drains. If the trap becomes dry, the roaches will travel up through the sewer pipes. To prevent this, floor drains should be flushed every week or so to recharge the trap. One way to keep floor drains from drying out is to add 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. Cockroaches can also end up inside buildings when a primary sewer line backs up, flushing roaches into businesses or homes.

Contact Colonial to have one of our pest control experts identify your cockroach. [A wood cockroach is another possibility although they are lighter in color and not as large.] A pest control company can treat your home for American cockroaches but if the problem is originating in the sewer system, treating your home will not provide a permanent solution.

In some instances, American cockroach problems can become so bad that populations in sewers will need to be controlled, but this can be complicated because treatment will have to be coordinated and authorized by the sewer system operator (which could be the Public Works Department, Water and Sewer Department, Sanitary Commission, etc.)

For more information on the American cockroach, look under Cockroaches in our Pest Library.