Research in entomopathology has always given more interest to biting insects, especially blood-sucking ones, the latter being vectors of serious and even fatal diseases. The mosquito would be for example the animal causing the most human victims in the world. The pathological involvement of other insects first harmless being still very little studied, a new study published in the journal Insects highlighted how the housefly can potentially pose a greater threat to humans (than the mosquito). Consuming exclusively liquid, this insect would vomit on food to predigest it and might therefore carry dangerous pathogens.
Worldwide, there are more than 80,000 different species of flies, whose morphology varies considerably from one species to another. Some can bite and feed on human or animal blood, tearing off (with their mandibles) a piece of flesh to access the capillaries. Others feed only on the flesh torn off by decomposing it or simply feed on decomposing organic matter. Some also have a very specific diet, such as the cherry fly, which, as its name suggests, feeds exclusively on cherries.
Housefly: potentially more dangerous than mosquitoes
Lacking mandibles, “non-biting” flies feed exclusively on liquid. Upon landing on solid food, they would first vomit a mixture of saliva and pre-digested food remains, in order to pre-decompose them and suck them up by taking them drop by drop with their paws.
According to researchers from the University of Massachusetts, the housefly would be the most to be feared, because being omnivorous, it lands and feeds on anything that can provide it with nutrients and energy. Present in abundance both in the countryside and in urban areas, it can land on fresh or spoiled food, on secretions of patients, on stools, etc. It is particularly attracted to heat and certain odors such as those of sugar and decomposition.
Each time they eat, they regurgitate part of what they have previously consumed, including pathogens (contained for example in droppings). They fill a kind of pocket like a reservoir, which would serve mainly as a place of storage and not of digestion. This pocket serves them both as a reservoir of enzymes, which they spit out to pre-decompose their food, and as a reservoir of food — which will then pass into another pocket intended for digestion.
The pathogenic agents that they can suck up are therefore not completely digested, the storage pocket being provided with only a few enzymes. Namely also that they are covered with all the decomposed matter on which they land (and then land on us or on our food). Although blood-sucking flies and other biting insects with direct access to the bloodstream are often deemed more dangerous, “we must be careful of those that live among us, as they derive their nutrients from people and animals that release pathogens into their tears, their excrement and their wounds,” warns John Stoffolano, professor of entomology at the University of Massachusetts and lead author of the study.
Because of this, the housefly can easily carry diseases such as cholera, salmonellosis, typhoid, tuberculosis, etc. Additionally, some flies that have developed resistance to insecticides might harbor antibiotic-resistant pathogens.
An important member of the ecosystem
It should however be noted that despite the generally negative perception that we have of the fly, it is part of an important ecosystem service. Due to its consumption of decaying organic matter, it plays an important role in the elimination of waste, which later feeds other insects or brings nutrients to the soil for plants. The fly is also one of the pollinators and contributes to the reproductive cycle of plants.
On the other hand, it is also part of a food chain that includes many species, such as birds, batrachians, arachnids, etc. Seeking to eradicate it would thus disturb a fundamental balance established in the biosphere for thousands of years.