"This is a male horse fly (Tabanidae) in the genus Hybomitra. It is one of the "red-sided" species of which there are several.
It might be Hybomitra lasiophthalma, but there are several "red-sided" species in the eastern US. They commonly hover along forest trails hoping a female might come by.
Sometimes there may be a number of them in a particular area, and they like to hover in shafts of sunlight." - JBurger,
Pikes Bridge Rd., West Newbury, MA
https://bugguide.net/node/view/240545