I don't think it is true that bottle flies or other will only lay their eggs in carcasses. I've seen maggots all over the farm, in manure, in the compost pile, common garbage. All they need is warmth, moisture and something that rots.
http://www.idph.state.il.us/envhealth/pcfilthflies.htm "House Fly (Musca domestica)
The common house fly is a dull gray fly, ¼-inch long with four dark stripes on the middle section (thorax) of its body. House flies typically lay eggs on animal feces and garbage. White, legless maggots (the larval stage) hatch from the eggs and grow to about ½ inch. When fully grown, maggots crawl away from their food source to undergo the pupal stage. They form a dark brown cocoon, known as a puparium, and later emerge as adult house flies that can fly one or two miles in search of suitable egg-laying sites.
Blow Flies (Calliphoridae spp.)
Blow flies are so-called because the larvae develop inside the bodies of dead animals, causing the carrion to have a bloated appearance. They also are attracted to garbage. Blow flies are about the size of house flies or slightly larger. They have been called “bottle flies” because their shiny blue and green color resemble colored glass bottles, though some species are shiny black or bronze. Large numbers of these flies indoors usually indicates the presence of a dead animal such as a mouse or bird inside the structure.
Flesh Flies (Sarcophagidae spp.)
Appropriately named, flesh flies usually seek carrion or scraps of meat on which to lay their eggs. Like house flies, adult flesh flies are dark-colored (gray or black). Common species have three dark stripes on the thorax. They are slightly larger than house flies and have a checkerboard pattern on the abdomen."
http://en.wikipedia.org/wiki/Blowflies
Adult blow-flies are occasional pollinators, being attracted to flowers with a strong odor resembling rotting meat, such as the American pawpaw or Dead Horse Arum. There is little doubt that these flies utilize nectar as a source of carbohydrates to fuel flight..
Larvae of most species are scavengers of carrion and dung and most likely constitute the majority of the maggots found in such material, although it is not uncommon for them to be found in close associate with other dipterous larvae from the families Sarcophagidae, Muscidae, and many other acalyptrate muscoid flies.
http://www.extension.umn.edu/distribution/housingandclothing/DK7568.html
Blow flies... lay eggs on garbage containing meat scraps, as well as on dead animals and animal wounds. They may also deposit eggs onto feces-caked hair or wool on pets and other domestic animals.
http://www.encyclopedia.com/doc/1E1-blowfly.html
...The eggs are laid on the material that serves as food for the larvae, e.g., decaying flesh and other organic matter. ...
http://lancaster.unl.edu/pest/resources/blowflies.shtml
...Bottle or blow flies lay eggs in decomposing organic matter, like garbage, animal manure, decaying vegetables, grass clippings and poorly managed compost piles. These flies are important in nature in the decay process of animal carcasses and are usually the first insects to arrive—within hours or even minutes—after an animal dies...
So it seems that they aren't too picky.
I am British but came across this case by chance whilst following US news items about your recent election.
