Belongs to: flies

St Mark's fly Bibio marci

Best time to see: late Apr to end May

Key facts

A large black fly, appearing in large numbers around St Mark's day, April 25th

Widespread and common in rough grassland, hedgerows and pond margins

Believed to be important pollinators of fruit trees


Large bulbous eyes distinguish the males from the females

Fly sluggishly with legs dangling


Larvae feed on the roots of grasses and decaying plant material, often in compost heaps

Emerge around the end of April, climbing up plant stems and bushes looking for mates

© Tony Gunton