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It looks, from a distance, like smoke rising from the ground without any sign of fire. Once you get a little closer though, it becomes clear that this isn’t smoke, but hundreds of thousands of flies. You might think that walking through them would result in you coming out the other end with hundreds of red spots where you’ve been bitten, but that is not the case. Where could this spectacle be occurring? Madagascar? Texas? Australia? Where ever it is, it has to be somewhere warm and tropical, right?

Well, it’s a lot closer than you’d think. This happens every year around the UK but some of the biggest swarms can be found at a loch in central Scotland. Loch Leven National Nature Reserve is host to huge swarms of non-biting midges that can appear and disappear in just a few days.

A non-biting midge, also called a Chironomid, starts off its life as a larva (aka. Bloodworms) living at the bottom of the loch, feeding on detritus but also being fed on by fish that are higher up in the food chain such as carp. In some places the densities of larvae can reach 4000 per square foot, so it’s no wonder there are such huge swarms around Loch Leven.

When the adults spawn from the water, they do so en masse because the sole purpose of an adult Chironomid is to mate and produce the next generation of non-biting midges. They don’t feed and they don’t live long, usually about 3-5 days, therefore the swarms can be there one week and be gone the next. Once an adult has mated and the eggs have been laid, they die.

In mid-summer, when the conditions are ideal, the life cycle can take place in a matter of weeks so one period of swarms can be followed by another a fortnight later. However, at Loch Leven there is more than one species of Chironomid and they have different spawning times so spawning times of different species may overlap. Loch Leven is a naturally eutrophic (nutrient-rich) loch which is exactly the habitat that Chironomids like. Loch Leven even has its own species that is found nowhere else on the planet, called cladontanypatrsus donmcbeani.

Loch Leven is managed by Scottish Natural Heritage as a National Nature Reserve due to the fact it is so rich in wildlife, and these flies are certainly no exception. If you come to the reserve to see what is a truly spectacular natural event, then it is easy to see how much the rest of the ecosystem benefits from their presence.

Birds such as Swallows, martins and swifts can sear through the sky with their mouths open, dabbling ducks can filter flies off the surface of the water, dragonflies and damselflies certainly don’t need to worry about where their next meal is coming from, and the flies that land on the surface of rivers, ponds and the loch feed fish such as brown trout, for which Loch Leven is famous for as a fishery.

So if you’re cycling or walking around the loch, swatting your way through a thick, humming mist of non-biting midges, just keep in mind that the wildlife around you is benefiting greatly from this abundance of food!