The German cockroach (Blatella germanica) is a species of cockroach under the order Blattodea commonly found all over the world. Related to the common wood termite, the German cockroach is the most commonly encountered pest variant of cockroach in the United States, next to the Asian cockroach, American cockroach, and the brown-banded cockroach.
The cosmopolitan nature of the species has caused many cultures to adopt different names for it. (Ironically, in Germany, the German cockroach is called the “Russian” cockroach). German cockroaches are dependent on human activity for their survival, so they are univocally found in centers of human populations. They prefer damp dark spaces, such as inside the walls or under the foundations of buildings.
German cockroaches are generally regarded by humans as pests and vermin; particularly resilient pests and vermin at that. That being said, blatella is of some entomological interest as the species exhibits remarkably sophisticated social behaviors, such as kin recognition, resource sharing, and chemical signaling processes. In fact, the German cockroach has the honorary title of being the first terrestrial species to conceive and reproduce in space, after a team of Russian engineers sent a roach they named “Nadezhda” aboard a research satellite. The species has also found use in the laboratory as a model organism, due to its ease of culturing and fast reproduction cycle.
Anatomy Of the German Cockroach
German cockroaches typically grow to be 1-1.5 centimeters and vary in color from a lighter brown to almost black. Despite their name, German cockroaches are thought to have originated from a region of Africa that is modern day Ethiopia. Like all species of cockroach, the German cockroach has a segmented body, 2 compound eyes, 2 long antennae located on the head, and a set of mandibles for chewing and secreting saliva on food. German cockroaches do have a pair of wings but unlike their close cousin the Asian cockroach, German cockroaches are incapable of true sustained flight, instead only being able to glide short distances.
German cockroaches are a dimorphic species, meaning that males and female have different appearances. Males tend to be smaller and more slender with a tapered abdomen, while females have rounded abdomens and are stouter.
German cockroaches are entirely dependent on human activity for survival, making them an inquiline species. Humans have primarily been responsible for their pan-ecological spread, as human travelers often take roaches with them. Blatella are omnivorous scavengers, meaning they will eat almost whatever they can get their jaws on. Primarily, they subsist off of the waste of humans and as such are commonly found in places such as restaurants, hotels, food processing plants, and communal locations; any location where there are typically a number of people producing waste. In times of famine, they will resort to the cannibalistic consumption of their dead. They are thigmotactic, meaning they react to stimuli mainly through touch. As such, they prefer tight enclosed spaces, as the physical contact allows them to keep their bearings.
Generally, German cockroaches are non-aggressive towards humans, preferring to stay out of our way and munch on any food we happen to leave out. When food supplies are scarce though, roaches are reported to bite humans, sometimes chewing at their fingernails or hands. The species has small mandibles and is nonvenomous, so any bite a human may incur is unlikely to be dangerous, apart from possible wound infection.
German cockroaches reproduce more quickly than any other known species of cockroach, with a larva reaching the stage of a reproductive adult in about 50-60 days. Slightly strange for an insect, female German cockroaches do not typically lay their eggs. Instead, they carry the eggs around in their abdomen until they mature. A female can birth one brood totaling up to 70 larvae nymphs in ideal conditions, though many of the larvae die before reaching sexual maturity. In a true display of nature’s cruel design, the high mortality rate of cockroach nymph’s serves an evolutionary purpose, as those dead nymphs become a food source for the nymphs that do survive. German cockroaches have no mating season, so they are continuously reproducing, resulting in many overlapping generations.
Like other insects, German cockroaches are gregarious creatures, meaning they thrive and depend on social interactions with others of their species. When hatched, newly born nymphs will naturally aggregate together, sharing resources and food. It has been found that when Blatella specimens are reared in isolation from other nymphs, their development processes are slowed and detrimentally affected. A widely cited study from 1964 determined that this aggregation of nymphs results from the presence of a particular hormone, secreted in the feces of the newly hatched nymphs.
In addition, adult cockroaches are able to distinguish members of their own reproductive line from other roaches. Each cockroach has a unique chemical profile secreted by cuticular hydrocarbons via antennae-to-antennae contact. The particular profile of the cuticular hydrocarbons serves as a sort of name tag, allowing the cockroaches to tell who is who. It is observed that this recognition mechanism has an effect on roach behavior; roaches prefer related roaches for social company but prefer non-sibling for mating purposes.
All of these behaviors are related to the German cockroaches general ability convey information via chemical signaling, an ability found in a number of insect species. German cockroaches have been found to signal the location of food sources, give signals about nearby predators, and choose partners for reproduction. The remarkable flexibility of their chemical signaling apparatus is due to a wide variety of chemoreceptor cells being encoded in its genome, resulting in the ability to sense a number of distinct chemical types.
Due to their scavenger-like nature, German cockroaches physical contact with a number of surfaces harboring pathogenic bacteria. As such, German cockroaches serve as potential disease vectors as bacteria can become stuck to their feet and be carried elsewhere. German cockroaches have been shown to carry strains of E. coli., Salmonella, and Staphylococcus aureus, the bacteria responsible for staph infections. So, populations of German cockroaches can be a public health concern.