German cockroaches have strict moisture requirements so infestations generally develop in kitchen and bathroom areas. Cockroaches often take up residence in warm cracks and crevices that are within five feet of a water source. German cockroaches are only active during the evening hours.

During the day, the cockroaches aggregate behind refrigerators, behind baseboard molding, in cracks around cabinets, closets or pantries, picture frames, and clocks or in cabinets, drawers, stoves, and dishwashers. German cockroaches spend about 75 percent of their time in these safe harborage areas. If cockroaches are seen aggregating in corners of the ceiling or other locations out in the open, it is a sign that the infestation has reached such a high level and that there are no secluded cockroach harborages available.

German cockroaches usually prefer a moist environment with a relatively high degree of warmth. As with other species, German cockroaches are mostly active at night, when they forage for food, water, and mates. During the day they hide in cracks and crevices and other dark sites that provide a warm and humid environment. Their relatively wide, flat bodies enable them to move in and out of cracks and narrow openings with ease.

Nymph has habits similar to those of adults. They are active mostly at night but hide in dark crevices during the day. If German cockroaches are seen during day, the population is probably so large that the available cracks are already full, or food and moisture are in such short supply that daytime foraging is necessary. Such behavior indicates that the population is under considerable stress. This species usually hides in areas close to moisture and food, which means the cockroaches are generally found in kitchen and other food areas. They prefer to rest on wood rather than on metal or other smooth surfaces. If water is present adult can live about month without food, but young nymph will die of starvation within 10 days.

The German cockroach is a general feeder but is particularly attracted to fermented foods and beverages residues. They eat food of all kinds and may hitchhike into the home on egg cartons, soft drink cartons, sacks of potatoes or onions, used furniture, beer cases etc..

• German cockroaches produce odorous secretions that can affect the flavor of various foods. When cockroach populations are high, these secretions may result in a characteristic odor in the general region of the infestation.
• Cockroaches have many negative consequences for human health because certain proteins (called allergens) found in cockroach feces, saliva and body parts can cause allergic reactions or trigger asthma symptoms, especially in children.
• Cockroaches can also passively transport microbes on their body surfaces including pathogens that are potentially dangerous to humans. Cockroaches have been implicated in the spread 33 kinds of bacteria, including E. coli and Salmonella species, six parasitic worms and more than seven other types of human pathogens.
• E. coli and Salmonella are classic causes of food poisoning, or gastroenteritis. Common symptoms include belly pain, severe stomach cramps and tenderness, diarrhea which can sometimes be bloody, nausea and vomiting. Some people can experience severe diarrhea, which will cause dehydration and may require hospitalization. In rare cases, the bacteria can spread to the blood stream and cause life threatening infections.