A WILDLIFE expert has reassured York residents that swarms of flies spotted in the city are harmless. Terry Smithson, head of conservation at the Yorkshire Wildlife Trust, said the sudden influx of the insects was natural and part of the food chain.

He said the increase of flies was probably due to the sudden appearance of the warmer weather after an unusually cold spring.

Mr Smithson said the type of fly is believed to be the St Mark’s Fly which appears around the saints feast day every year on April 25.

It often occurs in swarms and is normally only present in one area for a few weeks.