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The German cockroach (Blattella germanica) is a small species of cockroach, measuring about 1.3 to 1.6 cm (0.51 to 0.63 in) long; however, larger individuals have been recorded. It can be tan through brown to almost black, and has two dark parallel streaks running from the head to the base of the wings. Although it has wings, it is unable to sustain flight. Found throughout many human settlements, these insects are particularly associated with restaurants, food processing facilities, hotels, and nursing homes. In colder climates, they are found only near human habitats, since they are not very tolerant to cold. However, German cockroaches have been found as far north as Alert, Nunavut, and as far south as southern Patagonia. The German cockroach is originally from Africa. It is very closely related to the Asian cockroach, and to the casual observer they appear nearly identical and may be mistaken for each other (the Asian cockroach, however, is attracted to light and is capable of flight not unlike a moth— not so of the German cockroach). Though nocturnal, this cockroach can be seen in the day occasionally, especially if the population is large or they have been disturbed. However, sightings are most commonly reported in the evening hours, as they are most active at night. This type of cockroach can emit an unpleasant odor when excited or frightened.
The German cockroach is cosmopolitan in distribution, occurring as a household pest around the world. Previously thought to be a native of Europe, it is now is thought to be native to Ethiopia or elsewhere in northern Africa, and widely spread since ancient times. In Germany it is known as the Russian roach.
The German cockroach reproduces faster than any other residential cockroach, going from egg to sexually mature adult in approximately 123 days. Once fertilized, a female German cockroach develops an ootheca on her abdomen which will swell as her eggs develop. Once the translucent tip of the ootheca protrudes from the end of her abdomen, the eggs inside are fully developed. The ootheca will soon turn white, and then pink a few hours later. Within 48 hours of this it will shift to light brown and finally chestnut. As the ootheca has a "keel", it will noticeably curl to the left or the right as it nears final maturation. A very small percentage of the nymphs may hatch while the ootheca is still attached to the female, but remainder and the vast majority (>90%) will emerge within 24 hours after it has detached from the female's body. The newly-hatch 3mm-long black nymphs will then progress through six or seven instars before becoming sexually mature themselves, though each molting is so traumatic that nearly half of all nymphs simply die of natural causes before reaching adulthood. Molted skins are quickly eaten by the nymph that produced it or by others nearby at the time of molting.
The German cockroach is very successful at establishing an ecological niche in buildings, and is hardy and resilient against attempts at pest control. Some sources of this resiliency are the lack of natural predators in a human habitat, the large number of nymphs produced from each ootheca case, the short period between birth and sexual maturity, and the roaches' ability to easily hide. German cockroaches are thigmotactic, meaning they prefer close spaces, and small compared to other species, which makes them adept at fitting into small cracks and crevices, thereby evading humans and eradication efforts. Cracks and crevices near harborages are thus an effective placement for baits. However pest control methods must kill 95% of the overall population to be effective in a property due to the species' fast reproductive cycle.
Other considerations for controlling German cockroach populations are the interactions between individuals. Females carry their oothecae containing 18-50 eggs (average of 32) on the ends of their abdomens during germination until just before hatching rather than depositing them like other species, a practice which would leave the eggs vulnerable to predation. After hatching, nymphs can survive by consuming excretions and moults from adults and thereby remain hidden from most insecticidal surface treatments.
As a consequence of pest control using sweet poison baits, German cockroaches that experience glucose as bitter are becoming more common, resulting in refusal to eat the baits. In the past, sweet-tasting baits attracted cockroaches that could sense sugar, causing them to consume the bait and die, whereas those experiencing sugar as bitter avoided the baits and so lived to reproduce. As a trade-off for this sugar aversion, these cockroaches take longer to grow and reproduce.
The German cockroach is omnivorous and a scavenger. They particularly like starch, sugary foods, grease and meats. In certain situations where there is a shortage of foodstuffs, they may eat household items such as soap, glue and toothpaste or they may even turn cannibalistic, often chewing on the wings and legs of each other.
Comparison of three common cockroaches
|Cockroach||German cockroach||Oriental cockroach||American cockroach|
|Size||12 to 15 mm (1.2 to 1.5 cm)||25 to 30 mm (2.5 to 3.0 cm)||28 to 43 mm (2.8 to 4.3 cm)|
|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||No||Yes||Yes|
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