German cockroach (Blattella germanica) is the most troublesome and widespread species in the United States. They are usually introduced to a home through boxes, cartons, grocery and produce bags, and most commonly in second hand appliances.
Adult German cockroaches are tan to medium brown in color with two dark stripes on the pronotum. Though fairly small in size (10-15 mm), they reproduce very fast. The species can disperse in large numbers from areas of high population densities to new locations.
Adult German cockroaches, immature nymphs and egg case
Living up to 6-7 months, females produce a total of six to eight egg cases; each contains about 30 young roaches. The species usually carries the egg case on them until 1 or 2 days prior to hatching. Immature nymphs reach maturity in about 40 to 125 days.
German cockroaches prefer warm places (70° to 75°F): kitchens, bathrooms, food preparation and storage areas. They are attracted to sweet and floury foods. They also eat non-organic items such as toothpaste and books.
Besides being an unpleasant nuisance, German cockroaches produce filth materials that can trigger allergies leading to asthma in some people. This species is the major focus of control measures for residents and business owners.
It is difficult to eradicate the German cockroaches. Relying on a single strategy (e.g., spays) cannot bring success. It requires using several types of control tactics such as sanitation, getting rid of clutter, eliminating water and food, and effective bait products.
Oriental cockroaches (Blatta orientalis) are medium to large in size (1.5 inches or 26-30 mm) and shiny, dark brown or black in color. Females do not have wings (or rudimentary only), while wings on males are well-developed and usually shorter than the body. However, they move around mostly by crawling or running.
Oriental cockroaches, also called "water bugs", prefer wet, cool damp and dark places to hide in. They can be found in woodpiles, thick vegetation (especially junipers and ivy), and ground cover. Entering homes and buildings, they usually take shelter in garages, basements & crawl spaces, water meter boxes, drains, and under cement foundations and plastic covers. This species feeds on all types of garbage and organic material.
Adult Oriental cockroaches, immature nymphs and egg case
Females deposit dark red-brown egg cases in debris or food sites. Young immatures take 1 to 2 years or more to become full grown adult. Each female and her offspring can produce nearly 200 cockroaches in one year.
Oriental cockroaches produce a very strong smell. They are considered one of the dirtiest cockroaches. They differ from other species in that they cannot climb smooth surfaces. Very often, they are found trapped in jars, sinks, and bathtubs. Oriental cockroach can become a major problem if left uncontrolled.
American cockroaches (Periplaneta americana) are reddish brown in color and large in size (2 inches or 35-50 mm). Its protonum has light colored edges. This species prefers warm places in excess of 82°F and humid environments, such as: sewers, water meter boxes, storm drains, steam and subway tunnels, and animal-rearing facilities.
Adult American cockroaches, immature nymphs and egg case
They are very commonly associated to sewer and drain lines with access to new nesting areas. In favor conditions, they can migrate into outdoor environments. For this reason, they are common pests in zoos and animal farms. In addition to a good appetite for fermented foods, American cockroaches will eat anything, including plants and other insects. They usually live in the basement and ground floor of a building unless suitable conditions exist in higher locations.
American cockroaches can survive several years. Females carry the egg cases around for about 1 week and then glue them to a safe surface for incubation, as long as 45 days. Fresh cases are brown and turn black after 1 to 2 days, and each case can produce up to 12-14 young. Immature nymphs are reddish brown and wingless. Nymph matures in as little as 215 days to as long as 400 days. An adult female survives an average life span of about 440 days and, along with her offspring, can produce numerous cockroaches per year.
In our area, the American Cockroach is usually found in the sanitary sewer system, and do not pose an immediate problem for most people.
Pictures of cockroaches by courtesy of the University of Nebraska-Lincoln/Dept. of Entomology