The German cockroach (Blattella germanica) is a small species of cockroach, usually about 1.3 cm to 1.6 cm long, tan to light brown in color. The adults are winged, but do not fly. Originally from Africa, it is now the most common and most economically important household pest in the United States. They are common throughout the world, and although they are not cold tolerant they have been found even in the most northerly locations in close association with humans.
German cockroaches carry organisms that cause disease, principally bacteria, protozoans, and viruses that cause gut symptoms (food poisoning, dysentery, and diarrhea). They also produce malodorous secretions that taint the flavor of food, and their cast skins are allergens, but they are mostly aesthetic pests. Their flat bodies allow them to live in cracks and crevices of human habitations, often in large numbers. German cockroaches scavenge on any food, and even non-food stuffs such as soap and glue that are left around and are commonly found in garbage receptacles.
Mostly nocturnal, these insects are very hardy and resilient, and are difficult to exterminate. Females protect their young by holding their eggs in an ootheca until they hatch. Sanitation, keeping garbage containers sealed, putting food away and caulking holes in walls to limit access are helpful for controlling German cockroaches. Chemical baits and dusts are also used.
(Antani and Burgeson 2011; Jacobs 2007; Valles 2008; Wikipedia 2011)
German cockroaches, believed to have originated in Southeast Asia, are the most widely distributed urban pests. They have been introduced to all parts of the globe including North America, Australia, Africa, and the Oceanic Islands. This ubiquity makes German cockroaches cosmopolitan, with the only deterrent being cold temperatures.
Biogeographic Regions: nearctic (Introduced ); palearctic (Introduced ); oriental (Native ); ethiopian (Introduced ); neotropical (Introduced ); australian (Introduced ); oceanic islands (Introduced )
Other Geographic Terms: cosmopolitan
German cockroaches are ectothermic organisms. Adults measure 12.7 to 15.88 cm in length (average 13.0 cm) and weigh between 0.1 and 0.12 g (average 0.105 g). In general, German cockroaches are monomorphic with a flattened, oval shape, spiny legs, and long antennae. They are sexually dimorphic. Males have a thin and slender body, tapered posterior abdomen, visible terminal segments of the abdomen, and do not have tegmina (leathery outer wings). Females tend to be larger and have a stouter body, rounded posterior abdomen, and tegmina covering the entire abdomen. German cockroaches demonstrate bilateral symmetry at all stages of life.
German cockroaches are light brown in color with two broad, parallel stripes on the dorsal side of the body running lengthwise. Nymphal cockroaches resemble adults in shape; however, they are smaller, darker (dark brown to black), have only a single stripe down the dorsal side, and have undeveloped wings. Egg capsules are light tan and round.
Range mass: 0.1 to 0.120 g.
Average mass: 0.105 g.
Range length: 12.7 to 15.88 cm.
Average length: 13.0 cm.
Sexual Dimorphism: female larger; sexes shaped differently
Other Physical Features: ectothermic ; bilateral symmetry
German cockroaches live in temperate or tropical environments. They prefer warm, humid weather and are solely terrestrial. They inhabit a variety of habitats, from very moist areas, such as rainforests and scrub forests, to somewhat drier areas such as taigas and chaparrals. They are also found in sylvatic areas, such as forests and caves, as well as in urban, suburban, and rural settings. Cold is one of the major factors limiting the habitat of German cockroaches. On average, they are found at elevations of 1200 m, and, due to cold temperatures and dryness, they usually do not reside above 2000 m.
Range elevation: 0 to 2000 m.
Average elevation: 1200 m.
Habitat Regions: temperate ; tropical ; terrestrial
Terrestrial Biomes: taiga ; savanna or grassland ; chaparral ; forest ; rainforest ; scrub forest
Other Habitat Features: urban ; suburban ; agricultural ; caves
German cockroaches often reside in or around human residences due to the accumulation of garbage and detritus. They consume a wide variety of foods, including dead organisms. They usually eat human foods, especially starches, sweets, seeds, grains, grease, and meat products. German cockroaches have also been known to eat soap, toothpaste, and glue.
Animal Foods: carrion ; terrestrial non-insect arthropods
Plant Foods: seeds, grains, and nuts; fruit
Other Foods: detritus
Primary Diet: carnivore (Insectivore , Scavenger ); herbivore (Frugivore , Granivore ); detritivore
German cockroaches are prey to larger household pests. Because they consume detritus, they aid in the cycling of nutrients. They are also key hosts to parasitic bacteria, protozoans, and viruses, including Blatticola blattae, Hammershmidtiella disingi, Nephridiophaga blattellae, Gregarina blattarum, Lophomonas blattarum, Lophomonas striata, Endolimax blattae, Entamoeba thomsoni, and Nyctotherus ovalis. Some of these parasites utilize humans and other mammals as definitive hosts.
- Blatticola blattae
- Hammershmidtiella disingi
- Nephridiophaga blattellae
- Gregarina blattarum
- Lophomonas blattarum
- Lophomonas striata
- Endolimax blattae
- Entamoeba thomsoni
- Nyctotherus ovalis
German cockroaches are preyed upon by other household pests such as spiders and centipedes as well as domestic pets such as dogs and cats. German cockroaches can re-grow legs when necessary. They prolong their molting cycle to ensure that the new limb grows in during a molt. They also display aposematic coloring in the form of two stripes on their back. German cockroaches are relatively small and are able to hide in small crevices, cracks, and nooks. Nymphs can be as small as 0.7938 mm in width and adults as small as 4.7625 mm. Because of their size and nocturnal habits, they generally do not need to outrun predators.
- Spiders Araneae
- Centipedes Chilopoda
- domestic cats Felis sylvaticus
- domestic dogs Canis lupus familiarus
Anti-predator Adaptations: aposematic
Life History and Behavior
German cockroaches use their head ganglia to visually perceive their environment. They can also use their subesophageal ganglia to control thoracic fibers, which, when scraped against their body, produce minute noises. This functions as an alarm signal and allows others to escape predation. German cockroaches also use certain pheromones to signal activities such as feeding and evading predators, although these pheromones are generally used to signal mating.
Communication Channels: visual ; tactile ; acoustic ; chemical
Other Communication Modes: pheromones ; vibrations
Perception Channels: visual ; tactile ; acoustic ; vibrations ; chemical
German cockroaches have three developmental stages: egg, nymph, and adult. Females develop 4 to 8 capsules containing 30 to 48 eggs each in their lifetime. Capsules hatch about 28 days after they begins to form. A few weeks thereafter, a new egg capsule begins to form. The egg stage varies in duration from 14 to 35 days. German cockroaches have 6 to 7 nymphal stages occurring over a period of 6 to 31 weeks. They express incomplete metamorphosis: zygotes develop within eggs and hatch directly into nymphs, which then grow into adult cockroaches. The complete life cycle of the cockroach is roughly 100 to 200 days for females, during which 10,000 descendants of a single cockroach can be produced.
Development - Life Cycle: metamorphosis
Male German cockroaches, on average, live 100 to 150 days. Females live much longer, with an average lifespan of 190 to 200 days.
Status: wild: 180 to 200 days.
Status: wild: 100 to 200 days.
Status: wild: 140 days.
The mating behavior of German cockroaches is driven by pheromones given off by females, which are detected by the antennae of males. German cockroaches breed continuously with many overlapping generations present at any one time. As a result of continuous breeding and promiscuity, population growth has been shown to be exponential.
Mating System: polygynandrous (promiscuous)
German cockroaches are highly active sexually and breed continuously. Rate of breeding slows only during colder months. They breed throughout the year, mate indiscriminately and do not have cycles. They utilize internal fertilization, and females can store sperm for gradual release. When nymphs develop into adults, they become sexually active almost immediately. Females produce 4 to 6 capsules of 30 to 40 eggs each in their lifetime. Consequently, 3 to 4 generations may live together in a colony. Females lay 120 to 240 eggs per session (average 150 eggs), however, they are iteroparous and have multiple layings. Progeny are dioecious and hatch into nymphs in 25 to 30 days (average 28 days). German cockroaches reach independence between 40 and 150 days of age (average 65).
Breeding interval: German cockroaches breed almost continuously.
Breeding season: German cockroaches breed continuously year round, though breeding slows during colder months.
Range number of offspring: 120 to 240.
Average number of offspring: 150.
Range gestation period: 20 to 30 days.
Average gestation period: 28 days.
Range time to independence: 40 to 125 days.
Average time to independence: 65 days.
Key Reproductive Features: iteroparous ; year-round breeding ; gonochoric/gonochoristic/dioecious (sexes separate); sexual ; fertilization (Internal ); oviparous ; sperm-storing ; delayed fertilization
Females German cockroaches carry their eggs on their back for about 6 weeks before they are laid. They hide their eggs in discrete spots, such as cracks, holes, and dark places. They do not, however, provide parental care after eggs are laid.
Parental Investment: pre-hatching/birth (Protecting: Female)
Evolution and Systematics
Feet of insects stick to surfaces using nanometer-thin films of liquid secretions.
"Many insects cling to vertical and inverted surfaces with pads that adhere by nanometre-thin films of liquid secretion. This fluid is an emulsion, consisting of watery droplets in an oily continuous phase. The detailed function of its two-phasic nature has remained unclear. Here we show that the pad emulsion provides a mechanism that prevents insects from slipping on smooth substrates. We discovered that it is possible to manipulate the adhesive secretion in vivo using smooth polyimide substrates that selectively absorb its watery component. While thick layers of polyimide spin-coated onto glass removed all visible hydrophilic droplets, thin coatings left the emulsion in its typical form. Force measurements of stick insect pads sliding on these substrates demonstrated that the reduction of the watery phase resulted in a significant decrease in friction forces. Artificial control pads made of polydimethylsiloxane showed no difference when tested on the same substrates, confirming that the effect is caused by the insects’ fluid-based adhesive system. Our findings suggest that insect adhesive pads use emulsions with non-Newtonian properties, which may have been optimized by natural selection. Emulsions as adhesive secretions combine the benefits of ‘wet’ adhesion and resistance against shear forces." (Dirks et al. 2009)
Learn more about this functional adaptation.
Molecular Biology and Genetics
Barcode data: Blattella germanica
Below is a sequence of the barcode region Cytochrome oxidase subunit 1 (COI or COX1) from a member of the species.
See the BOLD taxonomy browser for more complete information about this specimen and other sequences.
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Download FASTA File
Statistics of barcoding coverage: Blattella germanica
Public Records: 12
Specimens with Barcodes: 22
Species With Barcodes: 1
As they are quite abundant, German cockroaches are not considered a species of concern in any part of their range.
US Federal List: no special status
CITES: no special status
State of Michigan List: no special status
Relevance to Humans and Ecosystems
Secretions of German cockroaches produce a foul odor when large colonies have amassed. These can also make human foods unpalatable. This can lead to considerable economic loss, especially in parts of the world where food is scarce or expensive. German cockroaches act as hosts to a number of parasites, such as bacteria, protozoans, and viruses, which lead to human ailments. Fouled food and parasites can lead to food poisoning, dysentery, and diarrhea in humans. Bodies, fragments, waste, and secretions of cockroaches are allergens to humans. These can lead to asthma in young children. Also, German cockroaches may bite humans, feed on particles on sleeping humans, and cause psychological stress.
Negative Impacts: injures humans (causes disease in humans , carries human disease); household pest
There are no known positive economic effects of German cockroaches on humans.
The German cockroach (Blattella germanica) is a small species of cockroach, typically about 1.1 to 1.6 cm (0.43 to 0.63 in) long. In colour it varies from tan to almost black, and it has two dark, roughly parallel, streaks on the pronotum running anteroposteriorly from behind the head to the base of the wings. Although Blattella germanica has wings, it can barely fly, although it may glide when disturbed. Of the few species of cockroach that are domestic pests, it probably is the most widely troublesome example. It is very closely related to the Asian cockroach, and to the casual observer the two appear nearly identical and may be mistaken for each other. However, the Asian cockroach is attracted to light and can fly rather like a moth, which the German cockroach can not.
Biology and pest status
Blattella germanica occurs widely in human buildings, but is particularly associated with restaurants, food processing facilities, hotels, and institutional establishments such as nursing homes. In cold climates, they occur only near human dwellings, because they cannot survive severe cold. However, even though they would soon die in the outdoors on their own, German cockroaches have been found as inquilines ("tenants") of human buildings as far north as Alert, Nunavut. Similarly, they have been found as far south as Southern Patagonia.
Previously thought to be a native of Europe, the German cockroach later was considered to have emerged from the region of Ethiopia in Northeast Africa, but more recent evidence suggests that it actually originated in Southeast Asia. Whatever the truth of the matter, the cockroach's sensitivity to cold might reflect its origin from such warm climates, and its spread as a domiciliary pest since ancient times has resulted from incidental human transport and shelter. The species now is cosmopolitan in distribution, occurring as a household pest on all continents except Antarctica, and on many major islands as well. It accordingly has been given various names in the cultures of many regions. For example, although it is widely known as the "German cockroach" in English-speaking countries, in Germany in turn, it is known as the Russian roach.
Though nocturnal, the German cockroach occasionally appears by day, especially if the population is crowded or has been disturbed. However, sightings are most frequent of an evening, when someone suddenly brings a light into a room deserted after dark, such as a kitchen where they have been scavenging. When excited or frightened, the species emits an unpleasant odor.
German cockroaches are omnivorous scavengers. They are attracted particularly to meats, starches, sugars and fatty foods. Where there is a shortage of foodstuffs, they may eat household items such as soap, glue and toothpaste. In famine conditions they turn cannibalistic, chewing at each other's wings and legs.
The German cockroach reproduces faster than any other residential cockroach, growing from egg to reproductive adult in approximately 123 days. Once fertilized, a female German cockroach develops an ootheca in her abdomen. The abdomen swells as her eggs develop, until the translucent tip of the ootheca begins to protrude from the end of her abdomen, and by that time the eggs inside are fully sized. The ootheca, at first translucent, soon turns white and then within a few hours it turns pink, progressively darkening until, some 48 hours later, it attains the dark red-brown of the shell of a chestnut. The ootheca has a keel-like ridge along the line where the young emerge, and curls slightly towards that edge as it completes its maturation. A small percentage of the nymphs may hatch while the ootheca is still attached to the female, but the majority emerge some 24 hours after it has detached from the female's body. The newly hatched 3mm-long black nymphs then progress through six or seven instars before becoming sexually mature, but ecdysis is such a hazardous process that nearly half the nymphs die of natural causes before reaching adulthood. Molted skins and dead nymphs are soon eaten by living nymphs present at the time of molting.
- lack of natural predators in a human habitat
- prolific reproduction
- short reproductive cycle
- sexual maturity attained within several weeks, and
- the ability to hide in very small refuges.
German cockroaches are thigmotactic, meaning that they prefer confined spaces, and they are small compared to other pest species, so they can hide within small cracks and crevices that are easy to overlook, thereby evading humans and their eradication efforts. Conversely, the seasoned pest controller is alert for cracks and crevices where it is likely to be profitable to place baits or spray surfaces.
To be effective control measures must be comprehensive, sustained and systematic; survival of just a few eggs is quite enough to regenerate a nearly exterminated pest population within a few generations, and re-colonisation from surrounding populations often is very rapid too.
Another problem in controlling German cockroaches is the nature of their population behaviour. Though they are not social and practise no organised maternal care, females carry oothecae of 18-50 eggs (average about 32) during incubation until just before hatching, instead of dropping them as most other species of cockroaches do. This protects the eggs from certain classes of predation. Then, after hatching, nymphs largely survive by consuming excretions and moults from adults, thereby establishing their own internal microbial populations and avoiding contact with most insecticidal surface treatments and baits. One effective control is insect growth regulators (IGRs; hydroprene, methoprene, etc.), which act by preventing molting and thus prevent maturation of the various instars. Caulking baseboards & around pipes may prevent the travel of adults from one apartment to another within a building.
As an adaptive consequence of pest control by poisoned sugar baits, a strain of German cockroaches has emerged that react to glucose as distastefully bitter. They refuse to eat sweetened baits, which presents an obstacle to their control, given that baits are an economical and effective means of control. It also is a dramatic illustration of adaptive selection; in the absence of poisoned sweet baits, attraction to sugars strongly promotes growth, energy and reproduction; cockroaches that are not attracted to sugars take longer to grow and reproduce, whereas in the presence of poisoned sugared baits it is sugar avoidance that promotes reproduction.
Comparison of three common cockroaches
|Cockroach||German cockroach||Oriental cockroach||American cockroach|
|Size||11 to 16 mm||25 to 30 mm||28 to 43 mm|
|Habitat||Heated buildings, optimum 32 °C (90 °F)||20 to 29 °C (68 to 84 °F)||Same as German|
|Nymphal development time||6 to 12 weeks||6 to 12 months||4 to 15 months|
|Lifespan||6 to 9 months||1.0 to 1.5 years||1.0 to 1.5 years|
|Able to fly||Barely||No||Yes|
- Blattellaquinone, a sex pheromone of the German cockroach
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