Plague of mating flies swarm Scottish beach just weeks after beetle invasion

Some of the swarms of flies on the beach in Scotland – many dead but others still moving (Picture: DGS/Cover Images)

Millions of swarming black flies have descended on the north of Scotland in a vast mating frenzy, just weeks after the same area was hit by an invasion of heather beetles.

Huge seething masses of insects were found washed up along the shoreline at Reiss beach, in Caithness, over the weekend, with millions more still alive and swarming inland.

The invasion appears to involve two species – fever flies (Dilophus febrilis) and the larger St Mark’s flies (Bibio marci), easily recognised by their long dangling legs.

Experts say the extraordinary numbers are linke...