With the winter being generally mild, there have been small swarms of winter gnats Trichocera sp. in the garden throughout, with their larvae probably feeding on the rotting leaves that we've piled up to make leaf mould.
Lately these long-legged little flies have gravitated towards the last few crab apples that are still hanging on the tree, gently rotting in the spring sunshine.
It's a convenient site for mating. When a female strays into the dancing swarms of males she's quickly captured ..... and so begins the next generation of winter gnats. The male is on the right.