Connectivity of green and blue infrastructures: living veins for biodiverse and healthy cities

Flies are cool

Flies are diverse, amazing, urbane, and some of them are the waste inspectors of the future.

When I moved to Paris, I decided that the animals that were easiest to observe in my daily life were flies, bees and ants. I therefore bought a guidebook to bees and ants of France, and another of European flies (which I had to specially order because apparently it wasn’t in high demand). Since then I have slowly become fascinated by flies.

First of all, I had long enjoyed beeflies (Bombyliids). You have to love an animal that, in English anyway, is two animals. While whale sharks, ant lions and mouse deer are all nice, they are not whalesharks, antlions, or mousedeer, which places beeflies at a strange axis of dualityambiguity. Beeflies are furry and hover. They have a kind of stubby head with extremely large compound eyes resembling a fencing helmet. Many bombylid species lay their eggs in flight, allowing them to fall near the nests of solitary bees, which the emerging larvae then pillage and predate. The other flies that resemble bees are the hoverflies (Syrphids), which are not furry but have yellow and black bands. They also hover. Their larvae eat a wide variety of things, including bee and ant larvae. Beeflies and hoverflies, like bees, can often be found drinking nectar from flowers, and thus are also flower pollinators. Beeflies and hoverflies, if not highly abundant, can certainly be found in urban parks.

The other day, on the seat next to me at a restaurant terrace, there was what might have been an Epitriputus maximus. It was black with a long abdomen, longer than its wings, shaped like a long pointy zigurat. Flying around my apartment I found a big, black, hairy, cobalt-bottomed Calliphora vomitoria. They visit both flowers and excrement, both of which can be found in my neighborhood (excrement of the dog kind). This is also the fly species whose larvae are used to clean out complex wounds. And at the park I noticed a lovely Anthomyia pluvialis, with red eyes, black and white marks on its thorax exactly like a retro colorblock trackjacket, and clear wings. The shiny green one with red eyes I also saw was probably a Lucilia ampullacea. Sitting on a yellow tulip I found two tiny black flies which I determined were probably Lauxaniids. I would love to see the strangely puffy, yellow Pegomyia silacea, which looks like a dried mulberry and can be found on flowers, or the gorgeous Phaonia pallida, with red eyes and a yellow-orange body finely speckled with red. It can be found on flowers, excrement and dead animals. Unfortunately, my guidebook puts it in humid and dense woodlands, so to get its decomposition and recycling services in the city will require the creation of some urban forests. The Oxyna parietina has a nice orange head with smallish eyes, a lovely-textured dark brown thorax and abdomen speckled with pale downy hairs, and clear wings tastefully mottled with brown. It lives in abandoned lots and near paths, so I might get to see it if I go to the right places. Thereva nobilitata is an amusingly-shaped fly, like a narrow American football (perhaps a nerfball). It has absurd reflective goggle-eyes, and is fuzzy and golden with transparent wings. It lives in moist grasslands, which sadly are rare in cities. I could go on.

Flies, when you pay attention to them, are ideal urban citizens. They are high-performance acrobats, due to their second pair of wings having evolved into stabilizing halteres. Their shapes, colors and textures are at least as interesting as, and often resemble, those of sports cars, motorcycles, technical apparel or haute couture. Some pollinate the flowers in urban parks while others help decompose material—like the compost in urban gardens— by laying eggs in it, which is then digested and broken down by their larvae. (And maybe its just me, but being a professional gardener while wearing haute couture and driving a luxury sports car sounds like a fantasy photoshoot--and flies do it every day.) Flies are also food for birds, bats, lizards, frogs, and other species that can find habitats in our cities, helping to sustain them as they go about their other kinds of ecosystem business.

The prejudice against flies is that they are dirty. Many species of fly are no more dirty than flowers, however. Flies that land on feces or carcasses, which certainly is not all species of fly, pick up pathogens from them, but there is little evidence that flies are human disease vectors. In a fascinating study (Junqueira et al. 2017), researchers proposed Chrysomya megacephala and Musca domestica as natural sampling devices for pathogens in the environment, which can be detected through genome sequences of the fly microbiomes. The researchers caution that “Clearly, the opportunistic and the potentially pathogenic bacteria identified in the blowfly and housefly microbiomes are not necessarily associated with a clinical condition or infection of a specific host, whether animal, plant, or human...The risk of infection ultimately depends on host susceptibility and contact with the agent transported by the [fly].” Other studies suggest that flies have the potential to transfer bacteria to humans when we are eating food outdoors, though less from contaminating the food itself and more from contaminating hands (through touching other objects that flies touched), food wrappings, plates and utensils. This suggests that cleaning your hands, and keeping wrappings, plates and utensils covered until use are basic precautions for eating in the presence of flies. The fly microbiome study “highlights the importance of surveillance of fly microbiomes, especially in densely populated areas. If included in public health surveillance programs, it will be possible to predict and prevent routes of transmission of microbes and potential pathogens mediated by..[flies].” Thus, the microbiomes of waste-visiting flies are a potential warning system for pathogen presence--the tiny urban waste inspectors of the future. I particularly draw your attention to the marvelous Figure 7 from this paper (see images above), in which researchers asked flies to first walk across an E. coli lawn and then across a fresh plate of agar, leaving what appear to be ski tracks made of transferred E. coli. Apparently, flies use their middle legs to punt themselves while gliding along their front and back feet. I had no idea. Flies are amazing.

Note: The two figures are from Junqueira et al. (2017).


Junqueira, A. C. M., Ratan, A., Acerbi, E., Drautz-Moses, D. I., Premkrishnan, B. N., Costea, P. I., ... & Subramanian, P. (2017). The microbiomes of blowflies and houseflies as bacterial transmission reservoirs. Scientific reports, 7(1), 16324.

Nelson, W., & Harris, B. (2006). Flies, fingers, fomites, and food. Campylobacteriosis in New Zealand--food-associated rather than food-borne. The New Zealand Medical Journal (Online), 119(1240).

Barro, N., Aly, S., Tidiane, O. C. A., & Sababenedjo, T. A. (2006). Carriage of bacteria by proboscises, legs, and feces of two species of flies in street food vending sites in Ouagadougou, Burkina Faso. Journal of food protection, 69(8), 2007-2010.

--Meredith Root-Bernstein 2019