Mayflies have an unusual life cycle and typically spend 2 years living in rivers, streams or lakes as a nymph. They then emerge in their adult form and often create mating swarms above the water. However, this adult stage is short-lived and typically only lasts for a day or two. As a result of this short life span, the adult Mayfly doesn't actually eat. Its sole purpose is reproduction!
I believe this individual is Ephemera danica, one of the UK's most common species of Mayfly.
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