Won't work.

To get rid of the flies, mix the foodstuffs into the pile.

The only reason you would have flies around your compost is because "stuff" they can easily eat is available. The only reason people have maggots in their compost is because there is a food source for the adults and sufficient moisture for the fly larva, the maggots, to hatch and live and that is too much moisture for the bacteria in the compost to properly work.
Since the penny is sealed inside the plastic bag any repellent properties that might be there would be sealed inside the plastic also and unavailable to the environment. As Jean said, "Won't work."

Well, I just checked my compost this morning and the flies are still gone, from the compost anyways. As I mentioned in my post, I did make changes to get rid of the food source (I also added browns to soak up some moisture). I'm sure getting rid of the food source helped to get rid of the flies, but within 15 minutes, I doubt it. I'm going to keep experimenting with the baggies and see what happens. BTW, I think the penny is suppose to be for good luck. Who knows, lol.

Here is a link discussing the topic.

Here is a link that might be useful: hgtv

I don't know why it works but it sure seems to - at least in some limited fashion. They even had a story about it on the Discovery Channel once.

Down here in the boonies you often see the ziplock bag of water tacked up beside the door of just about every establishment from the gas station to the barber shop and the local cafe owner swears it works. Mama used to safety pin a small plastic coated bag to the screen doors every summer - we still had some flies but nothing like they could have been.

Folks here call them "hillbilly doorknockers". ;)

Dave

As samekid480 stated other changes were made at the time so more than likely those changes made things inhospitable to the flies and they left because of that. Sometimes things like that seem to work because the person putting them in place wants them to enough to see they work whether they do or not.

I'll try it, just to see. I put leftovers in my pile and let the flies come. THAT'S how I keep flies out of my house, and it works like a charm. I've seen maggots just once, inside a whole crumpled papertowel that was holding moisture. I don't want to BREED flies, but I think of my pile as a voluntary detention center.
If it works, I'll be amazed. But, who really knows what a fly is thinking--except maybe Jeff Goldblume.

I've hung a few more bags around my plant containers and porch. It really seems to be helping, although a few flies don't seem bothered at all. I do notice alot of wasp buzzing around and found out that wasp attack flies. So maybe, the wasp are attracted to the water. I'm a believer! I will keep the baggies hanging around even though it looks like I'm doing some type of voodoo.

petalpatsy, please let me know how it goes. I've never seen any maggots in my compost either or my garbage. Maybe we just can't see them, I don't know.

Hillbilly knockers! Lol!

Oh boy, if digdirt hadn't weighed in on this I would have just laughed it off. I might just try it for our back door, where my youngest used a pencil to make a hole in the screen my husband had just installed. Now DH is mad and won't put in a new one, so the door has to stay closed.

Anyway what I really wanted to say was, wasps do like water, they use it to build their nests.

sufficient moisture for the fly larva, the maggots, to hatch and live and that is too much moisture for the bacteria in the compost to properly work.

Every time you post that I am going to refute it. Its simply not true, no matter how many times you repeat it. I don't want fellow composters thinking their pile is too wet, unnecessarily adding dry browns when its probably not necessary.

Moist as a wrung out sponge, is moist enough to support fly larvae. The best way to discourage flies is to keep the food stuff buried deep under the browns, as everyone agrees. But the presences of larvae is NOT an indication that pile is "too" moist.

Every time JPW posts a refutation of Kimmsr's thesis that fly larvae means the compost is too wet, I am going to agree with her :-).

I, too, was looking for an answer about getting rid of flies in my compost, and I thought the water-in-a-bag recommendation here sounds too good to be true, but nonetheless quite fascinating.

I looked it up on the Discover Channel web site to see whether they've tested it on Mythbusters, and I found the following in an article about getting rid of pests.

'Fill some clear plastic bags with water and hang them in the area you're trying to keep fly-free.

'It won't help with mosquitoes or other winged nuisances, but some people claim it repels flies because of their interesting optics. Flies' compound eyes have thousands of facets that present them with a mosaic picture of the world, so they could consider the light refraction in the water confusing or dangerous.'

I still don't know whether I believe it, but this is at least a plausible explanation.

Here is a link that might be useful: Discover Channel article about using water to repel flies