· by Michael Blair, Nashville's Pest Control
Most people call every roach a roach, and most over-the-counter products treat them as one problem. In a Middle Tennessee house there are really two situations. One is a large roach that lives outdoors and wanders in, usually at night and usually one at a time. The other is a small roach that lives and breeds entirely indoors. The size of the insect you saw tells you most of what you need to know about which one you have, and it decides the treatment.
Telling them apart
The big ones are usually American or smokybrown cockroaches, reddish-brown to nearly black and well over an inch long, the insects people here call palmetto bugs or waterbugs. The dark, shiny oriental cockroach turns up too, in cooler damp spots. The small one is the German cockroach: about half an inch, light tan, with two dark stripes running lengthwise just behind the head.
Where you see them matters as much as what they look like. A big roach in a bathroom, a basement stairwell or near a door is typical of an outdoor species that came in. Small roaches in the kitchen, around the dishwasher, the fridge motor or the cabinet hinges, especially in daylight, point to a German cockroach population that is already established.
- Over an inch, dark reddish-brown, seen singly at night: outdoor species
- About half an inch, tan, two stripes behind the head: German cockroach
- Small roaches seen in daytime: a large indoor population
- Egg cases or droppings like pepper in cabinet corners: breeding indoors
The big ones come from outside
Smokybrown and American roaches live in mulch beds, leaf litter, woodpiles, clogged gutters, tree holes and storm drains, and they move into vented crawl spaces when the weather turns. They rarely set up house in a dry, conditioned home. They come in through gaps around plumbing and wiring where it enters from the crawl space, under doors without sweeps, through foundation vents with torn screens, and up through floor drains and traps that have dried out.
That makes them an exterior and crawl-space problem. A perimeter treatment helps, but the lasting work is pulling mulch back from the foundation, keeping gutters flowing, drying out the crawl space, sealing pipe penetrations and fitting door sweeps. Running water into rarely used drains every few weeks keeps the trap seal full. The cool nights of October and the heavy fall rains both push these roaches toward shelter, which is why sightings often rise now.
The small ones live with you
German cockroaches do not survive well outdoors in our winters. They travel in: in grocery and delivery boxes, used appliances, secondhand furniture, luggage, and through shared walls in apartments and duplexes. Once inside they breed fast, carry their egg cases until the eggs are close to hatching, and hide in tight warm spaces close to food and water.
Spraying what you can see does very little, and foggers make it worse by scattering roaches deeper into walls without reaching the eggs. What works is gel bait placed in the harborage, combined with an insect growth regulator that stops the young from maturing, and repeated visits to catch each new hatch. Repellent sprays laid down near the bait keep roaches from eating it, so the two should not be mixed.
What that means for treatment
A quarterly exterior program is the right tool for the big outdoor species and does almost nothing for a German cockroach infestation inside the kitchen. A German roach cleanout is a targeted interior job over several weeks, and it is paired with the unglamorous part: food in sealed containers, crumbs cleaned from under the toaster and the stove, no pet food left out overnight, and leaks under the sink fixed.
If you are unsure what you are seeing, catch one on a sticky trap and look at it closely, or keep it for us to identify. It is the fastest way to avoid paying for a treatment aimed at the wrong insect.