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German cockroaches strongly prefer dark cracks and crevices, just big enough for them to squeeze through, ideally located with close access to food and moisture in a warm environment.

When walking through a food-processing facility, pest management professionals are trained to look for pests, evidence of pests and conditions that may lead to pests. Some of these pests do not try to hide from us. The adult stages of filth flies, small flies (such as fruit flies or drain flies) and ants usually make themselves known — it’s typically easy to see them when performing a thorough inspection.


However, some of our pests are cryptobiotic, meaning they prefer to live hidden. They are less likely to be spotted in an inspection unless their particular harborages are identified and inspected. German cockroaches show positive thigmotaxis — they feel safe and secure when both sides of their body are in direct contact with their surroundings. Due to this, German cockroaches strongly prefer dark cracks and crevices, just big enough for them to squeeze through, ideally located with close access to food and moisture in a warm environment.

If we are able to remove or limit those harborages, we succeed in making the facility less hospitable to German cockroaches, and the risk of infestation becomes much less. Our inspections can then focus on specific harborages that we cannot remove.


Unless your facility is designed with pest management in mind, once you start looking, German cockroach harborages can be anywhere. Those of highest priority will be those that are dark, warm, and close to a food and water source. Common harborages include:

  • Wall or Floor Juncture. Permanent equipment is typically attached to the floor and walls, typically with bolts (see Figure 1). The space between the floor/wall and equipment and even the bolt heads protruding from the equipment can all provide adequate harborage for German cockroaches.
  • Cracks in Floors and Walls. Cracks in floors and walls (see Figure 2 and Figure 4) are problematic for the pest management professional for several reasons. The first is that those cracks may allow entry into the facility from the outside. If not the outside, they may lead to a void underground or in the wall, where pests can populate, emerging from that crack. Cracks and crevices also collect food debris, if they’re in a food-processing environment, whether wet or dry.
  • Surfaces. Equipment in the food- processing environment, whether it’s responsible for processing food or not, is typically designed with as few cracks and crevices as possible, but there will always be places where food collects. These can be challenging to keep clean and inspected, particularly in facilities with 24/7 operation. Food debris easily settles in the crevices and nooks of equipment and depending on the equipment (such as electric control panels) can even build up substantially in voids. Regular routine cleaning, with pest management professionals brought in and/or when the equipment is shut down for inspection, can help locate those potential harborages.
  • Wall Overlays. Overlapping wall material, typically metal, corrugate or plastic, placed over concrete (see Figure 3 and Figure 5) is a very common spot for German cockroaches to harbor. We find this most commonly in moist environments, where the material is typically installed to ease cleaning. If not well sealed, that moisture and food can get trapped in between the different wall materials, providing a perfect habitat for German cockroaches.


Exclusion is one of the basic tenants of integrated pest management, yet we typically associate it with rodents. Exclusion principles can and should be applied to any pest. On the most basic level, it means excluding from entry — sealing up gaps that connect the exterior to the interior. But it also means removing those gaps that are providing harborage. As discussed, there are a lot of prime places to exclude for German cockroaches.

When excluding for German cockroaches, take the following steps to ensure a current small population does not become a future large problem:

  • Remove/Kill the Population. Before excluding, we must attempt to remove any populations that are currently using the harborage. If we simply seal over them, we run the risk of the population moving to another exit point and infesting another area of the facility. Depending on the size and accessibility of the void or crack to be excluded, a vacuum is typically a good start. We can remove most of the population this way without worrying about food safety risks that come with chemical means. If chemical solutions are necessary, baiting is typically the lowest risk and one of the most successful if we do not know how deep or big the crevice is. The bait that the German cockroaches consume will be brought by members of the population to the individuals that are hidden in the depths of the crevice, effectively killing the population. Residual insecticides and Ultra Low Volume (ULV) treatments also may make sense in some environments, but of course always follow the label when choosing and executing the appropriate strategy.
  • Sanitation. After the population is removed or killed, sanitation is important. Clean the crevice to remove food and debris, decreasing the attractiveness of the crevice. This will reduce the chances of German cockroaches inhabiting it in the future, as well as reducing the risks associated with pests and mold.
  • Seal. Once as clean and empty as possible, seal the crevice. There are many tools for sealing, so it is important to consider which is the correct one for the facility. Take the following into consideration when choosing the right sealant:
  • Size. For a small crevice just a few inches long, a caulk or sealant may work well, but for a larger crevice, it may make more sense to seal with a patch.
  • Cleanability. Does this area need to be regularly cleaned? Whatever sealant is chosen should allow for regular cleanability, whether that cleaning process is dry (vacuum) or wet. For example, if a metal filler mesh is used to fill the crack or void, it may be prudent to further seal over the mesh, to ensure that the area can be cleaned.
  • Permanence. It may make sense to seal around the legs of a permanent piece of equipment in a facility, but not a temporary piece. Consider how long that piece will stay put.
  • Food Safety. Depending on the area of the facility used, you may need to use a food-safe sealant.
  • Expandability. Particularly if the crevice is due to expansion (such as an expansion joint) choose a sealant that allows for the crevice to flex in size over time.


While German cockroach harborages may be the crevice of interest now, does that same void provide entry or harborage to rodents? Stored product pests? Flies? If so, consider that in your selection, you’ll want to choose the sealant that is most effective for all the pests that could potentially live there.


With those parameters in mind, choose the appropriate tool to seal the crevice. Bobby Corrigan, RMC Pest Management Consulting, provides an excellent overview of the qualities of various caulks and sealants in

“Recommendations for Selecting and Using Caulks and Sealants in Pest Management Operation.”

Over time, the seal may become worn and in need of replacing, depending on the environment it is in and the amount of use it gets. Seals need to be regularly examined to ensure they maintain their integrity. Often, we’ll find that seals are still in place, but not effective, serving to hide hidden German cockroach populations that travel in and out of the inadequate seal.

Anna Berry is a Board Certified Entomologist and technical manager at Terminix. Berry joined Terminix through the acquisition of McCloud Services, where she served as training manager and entomologist.