The presence of the midges - who do not feed as adults, and are only mating while in the swarm - is described as great news for local wildlife.
Gus Routledge, of Scottish Natural Heritage, posted his film on social media, stating: “I quite simply can’t get over how many non-biting midges are around Loch Leven. Swifts are loving it.
“It is pretty bonkers, looks like smoke above the paths, and they don’t have any discernible taste which is a bonus.”
He added: “I think this is absolutely brilliant and people should come down to see it. It’s an amazing spectacle to witness such a huge number of insects, especially when you think they are fuelling the rest of the ecosystem here.”
The path where the flies have hatched is about a 45-minute walk between the RSPB car park and Loch Leven’s Larder.
On the Loch Leven National Nature Reserve, Gus added: “They are non-biting midges, also called Chironomids, which is good news because the place would be inhospitable if they were bloodsuckers.
“I’m going to put up a few signs that explain some things about them around the reserve.
“Basically, they are of no harm to you or I other than occasionally getting in you eye or ear, but they are a huge help to many of the animals around Loch Leven.”