A guy that I know from work says that there are really large, flying roaches that live in sewers and can get into your home that way, through the sewer system. Is that true?

A. D., Blackstone, MA

It does happen. A couple of different cockroaches can live in sewers, but the American cockroach is the most common sewer roach. This roach is large, about 1-1/2 inches long, and it can fly. See Do the Roaches Suddenly Seem Bigger?

Home, Sweet Sewer!

From the cockroach’s viewpoint, a sewer is a perfect home. Roaches thrive in dank darkness, feeding on decaying organic matter and unmentionable things. An underground sewer system is insulated, warm in winter and cool in summer. A sewer provides protection from people and predators (with the possible exception of hungry rats). There is plenty of water and your dinner flows by in an endless buffet line of human waste and food scraps.

How Do They Get From Sewers Into Buildings?

Having cockroaches in a sewer system would not be a problem if they stayed put. But they don’t. American cockroaches have only one generation per year. In fall, the fully-grown nymphs tend to migrate, looking for food and places to spend the winter. They can simply leave the sewers by squeezing out of the vent holes in manhole covers and can then enter buildings nearby. Ongoing American cockroach infestations in commercial buildings are often traced back to the sewer system (see American Cockroaches Occupy Lower Levels of Buildings).

Sewer roaches can also find their way into buildings when a primary sewer line backs up, flushing thousands of roaches into homes or businesses. Heavy rains can drive cockroaches out of combined sewers into basements. Or, a drain trap can dry up and cockroaches can simply walk through the sewer pipes, through the trap and out the floor drain (see Cockroaches From Sewers).

When cockroaches are occupying sewer systems and, more importantly, escaping from sewer systems, solving the problem isn’t as easy as you would think. Treating the sewers with insecticides can become a political and regulatory issue, involving coordination with the sewer system authority which could be the Public Works Department, Water and Sewer Department, Sanitary Commission, Health Department, etc. And the older the sewer system, the more likely it is to be infested with cockroaches and rats, and the more difficult it will be to solve the problem.