Flies carry germs

Entomology: There are so many germs in flies

Around 100 different invertebrate species live in every average household - this was shown by a study in "Scientific Reports". The houseflies and blowflies are certainly among the best known and least popular of these roommates. They not only buzz around the food, but are also considered to be carriers of all kinds of pathogens. Another publication in the "Scientific Reports" shows that they do this job even better than previously assumed. Ana Carolina Junqueira from the State University of Rio de Janeiro and her team examined 116 houseflies and blowflies from three continents and from different human environments with regard to the bacterial load that the animals carry around with them.

In total, the scientists were able to detect 316 different types of bacteria on the blowflies and even 351 on the house flies, whereby individual specimens could actually be on the move with several hundred types of germs each. Naturally, the highest density was found in the legs with which the animals stand on faeces or carrion, but the wings were also heavily contaminated. "The bacteria use the flies like a taxi," says the participating biologist Stephan Schuster. The bacteria found included numerous pathogens that can cause severe diarrhea or other malaises in humans. There were even flies from Brazil Helicobacter pylori around, which can cause stomach ulcers in those affected - as a potential vector, however, these insects have not yet been targeted, warns Schuster. Around half of all bacteria were found in both house and blowflies, which is not surprising given their similar food preferences. Both look for carrion and feces to lay their eggs and to feed.

Surprisingly, the researchers found strong urban-rural contrasts: In densely populated regions, the flies had more bacteria than their fellow species that were caught in the vicinity of cattle stalls in the countryside. Obviously, access to open latrines or septic tanks is an important source of human pathogens on insects, while livestock keeping promotes the number of flies itself, but exposes them to bacteria that are critical for us less. In the future, this could perhaps be taken into account when choosing a picnic area, says Schneider - in a forest clearing you expose yourself to lower risks from flies than perhaps in a city park.

Despite the high disgust factor, the biologists also see a positive side aspect: the flies could serve as simple bioindicators. Their bacteria could be used to determine where pathogens could be present in defined areas. Because of their small size, they penetrate areas that are practically closed to people - where carrion rots, for example.