Insects, Sketchbook

St Mark’s Fly- Bibio marci

This species of fly is one I look out for each year at the end of April. It is called St Mark’s fly because it first emerges to perform its mating flight around St Mark’s day which is 25th April. Each year I am astonished at how accurate this date is for first observing them. They are slightly menacing black flies, flying repeatedly up and down around hedges and undergrowth in great numbers with their legs dangling almost like ropes from a helicopter. This is the time they mate and once the eggs are fertilised the female will lay them in the ground and then die. When these eggs hatch the larvae will feed on rotting vegetation and roots through the autumn and winter. Around St Mark’s day they emerge as the adult fly ready to breed. They are thought to be important pollinators. For me the St Mark’s fly is as much part of the season as the first Swallow and I love watching them dancing in the air during their short adult life.

St Mark's flies and Oil Seed Rape- watercolour in sketchbook
Male St Mark's Fly, 28th April- photograph by Jonathan Pomroy

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