Family: Blattidae, Blattellidae
Cockroaches can feed on a wide variety of food sources but tend to prefer foods containing meat and starch.
The American cockroach (Periplaneta americana) measures up to 5 cm (2 inches) long as an adult, and is the largest pest species in Colorado. While they do occasionally invade homes, these cockroaches are most likely to be encountered in warm, moist areas like furnace rooms, sewers, and heat tunnels of industrial or commercial buildings. The species is mahogany in color with a yellow margin around the head and upper surface of the segment between the wings and head (i.e., prothorax).
The German cockroach (Blattella germanica) is a relatively small insect, measuring about 1.3 cm (0.5 inch) as a fully grown adult. Typically, this species is associated with buildings that store or process food. Infestations spread when German cockroaches migrate from infested buildings to nearby structures, or longer distances when they are transported in food containers. Preferred habitats in the home include warm, moist areas like kitchen sinks, appliances, bathroom sinks, and furnaces. These cockroaches have a pair of parallel brown lines on the prothorax between the head and base of the wings.
The brownbanded cockroach (Supella longipalpa) is similar in appearance to the German cockroach but lacks the brown bars on the segment between the wings and head. Unlike the German cockroach, this species tends to prefer locations with a warmer, drier environment such as ceilings, light fixtures, furniture, and appliances.
The oriental cockroach (Blatta orientalis) is much darker than the American and German cockroaches, and intermediate in size. In addition to producing a strong odor, adults have wings that do not extend to the end of the abdomen. It is most often found in cool, damp, dark areas such as sewer drains, damp crawl spaces, basements, and cellars. Infestations are most frequent in the spring and fall.
- There are over 50 cockroach species in the United States, but only four are likely to be found in Colorado. They are the German cockroach (Blattella germanica), American cockroach (Periplaneta americana), brownbanded cockroach (Supella longipalpa), and the oriental cockroach (Blatta orientalis).
- Preventative measures include eliminating sources of water, food, and hiding places to reduce the likelihood of an infestation.
- Cockroach saliva and fecal matter can trigger asthma attacks.
- Cockroaches are more active at night. Spotting cockroaches during the day is an indication of a heavy infestation. Cockroaches do not sting or bite.
- A combination of traps, insecticide sprays, and insecticide dusts can be used to manage or eliminate cockroaches.
American cockroach adult. Note the yellow margin on the prothorax between the head and base of the wings. Cockroaches are attracted to leftover food and other debris they can consume and use as shelter. Therefore, sanitation is a particularly good preventative measure to reduce the likelihood of cockroach infestations. Image credit: Jerrod Hein, Kansas State University, Bugwood.org
German cockroach adult. Note the two parallel dark lines running along the prothorax between the head and base of the wings. Image credit: Daniel R. Suiter, University of Georgia, Bugwood.org
Oriental cockroach laying an egg case. Note the dark color in comparison with the American and German cockroach. Image credit: Daniel R. Suiter, University of Georgia, Bugwood.org
Brownbanded cockroach adult. Unlike the German cockroach, this species does not have two dark bands on the prothorax between the head and base of the wings. Image credit: Gary Alpert, Harvard University, Bugwood.org
Newly molted American cockroach. The exoskeleton is soft and white immediately after molting. Image credit: Daniel R. Suiter, University of Georgia, Bugwood.org
Different nymphal stages of American cockroach. Image credit: Daniel R. Suiter, University of Georgia, Bugwood.org
The gap between the pipe and wall is a potential point of entry for cockroaches. Image credit: Liz Kasameyer, Johns Hopkins School of Public Health, Bugwood.org
Loose baseboard provides a suitable area for cockroach infestations. Image credit: Liz Kasameyer, Johns Hopkins School of Public Health, Bugwood.org
Life history and habits
All cockroaches have three life stages: egg, nymph, and adult. Eggs are laid in clusters and covered with a hardened protective layer forming characteristic cases (ootheca). They are bean shaped and contain 10-40 eggs, depending on the species. After emerging from the egg, nymphs are relatively small and wingless, but similar in shape and color to adults.
Cockroaches are most active at night, and typically rest and hide in cracks and crevices during the day. When cockroaches are observed in the daytime, this is usually an indication of a heavy infestation.
Prevention is an effective management approach for cockroaches. Weather stripping and caulking can reduce the available routes of entry when cockroaches are migrating to clean areas from infested parts of a building. Reduce the availability of hiding places such as caulk cracks and crevices in moist, dark areas, piles of newspaper, boxes, rags, or similar items. All items being brought into the clean area should be inspected, especially food containers, furniture, appliances, and clothing. While adults and nymphs are easy to spot, some cockroaches affix their eggs to various surfaces, so it is important to inspect closely for the presence of egg cases.
Cockroaches are typically found in areas with high moisture such as kitchens and bathrooms. Eliminate standing water by making the necessary plumbing repairs and modifications. Food should not be allowed to accumulate in unwashed dishes, pet dishes, pet food containers, litter boxes, waste containers, or under kitchen appliances like refrigerators, stoves, sinks, and furniture.
Detection is an important component of cockroach management. Since cockroaches congregate in certain sheltered locations, control measures should target these spots. While cockroach traps cannot eliminate established infestations, they can be an effective tool for monitoring its severity and help inform decisions related to additional treatments. The traps consist of small, open-ended boxes that contain an attractant and a sticky adhesive for capturing the insects once they enter. Place traps against walls under sinks, in cabinets, and in basements. Moving traps to another area if two nights pass without a capture is a common practice to ensure effective detection of the pests.
Many organisms attack cockroaches, including toads, bacteria, protozoa, beetles, mites, and wasps but biological control of cockroaches is not common in homes. In nonresidential buildings and warehouses, parasitic wasps have been used successfully to reduce cockroach numbers dramatically and suppress growth of the population.
Insecticides for cockroach management come in the form of insecticides, dusts, and baits. Effective control may require combining various treatments. Before use, it is important to read and follow all label instructions. While these insecticides are typically effective, resistant populations of German cockroach exist in some parts of the country and can limit the efficacy of insecticides.
Residual insecticide sprays deposit toxins on a surface that will kill cockroaches on contact for two to four weeks. These should be applied to cracks and crevices where cockroaches hide and forage. The surface should be sprayed until wet but avoid overapplying until puddling or runoff. Nonresidual insecticide sprays kill cockroaches on contact only and do not persist long. They can be effective when combined with residual treatments. Some of these aerosol insecticides irritate cockroaches and flush them out of their hiding places, forcing them into areas treated with a long-lasting residual insecticide. Flushing can also determine whether an infestation is present but may also drive cockroaches into uninfested parts of the building.
Insecticide dusts can penetrate cockroach hiding places and have a longer period of residual activity when applied to dry locations. Examples include boric acid powder, silica aerogel, or diatomaceous earth. Boric acid powder is a good cockroach insecticide and is relatively safe for humans. Silica aerogel and diatomaceous earth act as repellents and can be used to keep cockroaches out of certain areas.
Baits consisting of an attractant like peanut butter or syrup, and a nonrepellent insecticide such as boric acid are useful in areas that cannot be sprayed or dusted.
When an infestation is severe, or the best course of action is unclear, such situations may benefit from professional pest control services. Certified professionals will have access to insecticides and equipment that are not available to homeowners.
Davis, R. 2010. Cockroaches. Utah State University – Extension. Available https://digitalcommons.usu.edu/cgi/viewcontent.cgi?article=1878&context=extension_curall