Can peppermint oil get rid of flies?

Yes. Peppermint, although it has a pleasant aroma and taste to humans, is naturally disliked by many insects, including mosquitoes, fleas, ants and flies.

Some suggestions for using it as an insect repellent include strategic placement of cotton balls soaked in peppermint oil, topical application on the body, or the use of various concoctions containing peppermint oil that can be sprayed over a broader area.

A couple of links are given below, with more information.