It dovetails with human progress:
Once, houseflies emerged from horseshit by the billions. When that ran out (thanks to the invention of cars), they turned to our garbage and so we collected it more frequently and took it far away. When the garbage become rare (some places, though not everywhere), they found the dog waste we left behind in cities. And now that New Yorkers, for instance, in their fancy shoes and dark clothes, gather the dog poop in bags, the flies have found those places we have taken our waste to hide it from them (and from ourselves). At garbage dumps flies flock in dense halos. They are born too out of the rough parts of towns—smoke signals of neglect. They have even found the places we have moved our animals, the modern mangers of chickens and pigs where waste is dumped into vast pools.
The piece then takes an ominous turn to describe the threat that flies on factory farms pose when carrying new strains of bacteria resistent to antibiotics.
(Image by Marcus Moore)
The Dish 