I often see the statement made that maggots only eat dead flesh. Do maggots absolutely never eat healthy flesh, or is it just a general rule that they don’t? Will a starving maggot go without food rather than switch to healthy flesh?
Maggots are the larval stage of flies. Mommy fly will not deposit the eggs in a place she finds unsuitable for raising her young, I’d think. 
Oh, and the animal does not have to be dead, just the place where the maggots live has to be necrotic. Think nasty untreated infected wound. And of course, without treatment, that area may get bigger and bigger, but the maggots themselves are feasting on the dead part, not burrowing their way into the still viable flesh left.
There are a couple of flies whose larval stages can and will eat healthy, non necrotic flesh. One of them is Cochliomya omnivorax, a foreign parasite to the United States. There have been a couple of cases in which animals travelling abroad have come back with their larvae, but luckily all the maggots were removed before they grew up and reproduced, so they were not reintroduced to the environment.
I don’t have any cites handy, but I’m certain that maggots are sometimes used to clean wounds on humans. Maybe it was experimental?
I guess it wouldn’t be much different than using leeches to maintain blood flow in reattached fingers.
Given that surgical maggots are used to clean dead tissue from wounds, I’d say it’s a fairly strict rule. (And modern physicians still use leeches. There’s a distinct lack of coverage of black bile in Taber’s these days, though.)
I’m asking, because it’s used for cleaning up wounds and such. Will the maggots start eating healthy flesh when starving, because the hospital staff screwed up, and left them in place too long.
And a timely story. I suspect the fact that the woman might not make it has more to do with the advanced condition of the sore than the presence of maggots.
I’ve always wondered this. How do they “know” to eat only dead tissue?
Dead over live? Maybe the odor and the softer consistency make dead flesh more appetizing.
I made a huge typo with my screwworm post…
The correct name is Cochliomyia hominivorax, and this is the OIE chapter on both this species (New World) and Old World screwworm.
As it says there, unlike other types of flies, they specifically seek out live animals and lay eggs on their fresh wounds (or even undamaged skin, eek!). And unlike other flies which only feast on the rotting parts, these flies burrow deep into the living tissues, tearing them apart. All the while, they secrete odors that attract even more screwworm flies. Interesting reading, but it doesn’t deal with the other types of flies.
From what I’ve read, it seems they are attracted to the smell of decaying matter (and feces). That’s why they lay their eggs there.
A quote from the Merck Vet Manual regarding blowflies:
Their presence can create additional injury, but the maggots themselves are not tearing the flesh apart.
How do you “know” not to eat poop?
For both the Common Housefly and it’s larvae (maggot) the way they eat is by drinking! They release enzymes that liquefy the dead and decaying material then drink it up. They can’t eat live flesh because the enzymes can’t liquefy it.
BTW, the New World Screwfly is native to the southern US. However it was eradicated here.
Greenbottle maggots are used for maggot therapy because of their preference for necrotic tissue. It can be very successful. A friend of mine had the enviable title of “maggot nurse” in a UK hospital some years ago. According to her, most patients cope well with it as long as the maggots are covered and there are no escapees. :eek:
In contrast, other types of blowfly maggots do not discriminate between healthy and necrotic tissue. Fly strike is a common, often fatal, problem in many species.
Maggot therapy is used in the veterinary world, although I’ve never tried it. I’ve spent enough time picking and flushing them out of infected messy wounds, it just goes against the grain to shove more - albeit different - maggots in there. I have had some good results with leeches though, on one occasion saving a limb which we were resigned to amputating.
But do flies eat zombies?
I had always thought (no cite) that maggots used for medicinal purposes strongly prefer dead flesh and will preferentially eat that, but they aren’t gonna starve to death once the dead flesh is consumed.
As in, they are used to clean necrotic tissue from a wound, but are removed promptly once the necrotic flesh is mostly gone. Otherwise they’d just keep eating shudder.
But there’s a limit to how much a maggot will eat before pupating; they only live 4-7 days and would probably pupate if they run out of food.
BTW, the woman I linked to earlier did actually pull thru.
Some type of fly is responsible for ocular myiasis (in living tissue), which is always interesting to watch on medical docs.
I felt that was a very intelligent comment about the poop, Santa!
It could have been… three hundred years ago when a French battlefield doctor started using maggots to clean wounds 
(actually, according to Wiki the practice is even much older than that)
It might not be true of all maggots, but certainly there are species of flies whose larvae just don’t go in for healthy tissue, probably because of a consumption (can’t bite chunks off) or digestion (can’t process it) issue.
Of course they do - they are, by definition, dead.