Something to look out for this month.
The Dark-edged, or 'Large Bee-fly'
Bee-fly feeding on Alkanet at swan Lake Allotments. Bernard Baverstock©
There are two species of Bee-fly that you might see in the Blackwater Valley, the Darkedged or Large Bee-fly Bombylius major, the most common which has a strong dark mark across the front half of its wings and the rarer Dotted Bee-fly Bombylius discolor which has a spotty wing edge.
Dotted Bee-fly also has a darker body colour. This species is only found in the south of England but does sometimes occur in gardens.
The Dark-edged Bee-fly, looks rather like a small bumblebee with a long, straight proboscis that it uses to feed on nectar from spring flowers, such as primroses and violets. Although these look dangerous they are quite harmless. These bee mimics hum and hover in front of flowers like bees but, unlike bees, when they feed they perch on the flower with their long legs.
They have a very special and strange, life cycle.
The adults exhibit courtship rituals - males hover at height and exhibit territorial behaviour which includes darting at rival males and spinning at females.
The female Bee-fly will search for the nest of solitary bees and wasps then, while hovering, flicks her eggs towards the entrance holes. These get taken into the nest with the returning bee and once in the tunnel, the egg hatches and the worm-like maggot crawls into an open host cell. It remains inactive until the host larva is about to pupate. The bee-fly larva then becomes a maggot-like ectoparasite and attaches to the outside of the host, sucking out the body fluids. They will then over-winter and emerge in early Spring.
While you may find these intriguing creatures it is almost impossible to identify them while they are flying but easy enough when they settle.
Here are pictures of the Dark-edged and the Dotted to show the difference.