Specieswatch: St Mark’s fly enjoys a bumper 12 months | Bugs


T.This is a particularly good year for the St. Mark’s fly (Bibio marci). They were sometimes so numerous that it was quite difficult to avoid clouds from them. The flies you usually see are males, black and about 12 mm long, with large eyes and dangling legs that rock up and down about head height. The man’s eyes are split in two, one half to keep an eye out for the women who appear later and the other half to check how far they are from the ground. The females are slightly larger, but with smaller legs and eyes.

The fly’s name comes from the normal first appearance of males on St. Mark’s Day (April 25th), but this year the flocks came weeks later because of the cold spring. In places the flies are still numerous. An important fruit pollinator, they are also known as hawthorn fly as they often drink nectar from these flowers.

When the females emerge, they survive for about six days. During this time, they need to find a partner and lay their eggs in the ground. When the larvae hatch, they spend autumn and winter in the ground and live on rotting vegetation. The miracle is how both sexes manage to synchronize their short and energetic adult lives every spring.