I couldn’t resist spending some more time this spring watching bee-flies. I can combine this with a continuing study of a violet oil beetle population in a local meadow. Both of these insects are nest parasites of solitary bees. The oil beetle larva feeds on the pollen collected by the bee whilst the bee fly larva waits for the bee larva to consume its food supply before latching on to its body and sucking it dry!
A favoured spot for the dark-edged bee flies Bombylius major is a sheltered corner of the meadow around a large patch of primroses. On sunny days in March and April there are usually several bee flies nectaring in this area so it is just a matter of sitting and waiting for them to appear.
By early May the season is almost over at this site with just a few worn looking females egg laying. It is fascinating to watch them prop up themselves up with their delicate long legs and collect dust on special hairs at the tip of their abdomen. They then fly around low to the ground stopping occasionally to flick eggs in to likely spots for nesting solitary bees.
This year has been a good one for the bee-flies and oil beetles. My counts of oil beetles over the last four springs has gone down from 117 in 2010 to just 45 adults last spring. This was almost certainly due to the exceptionally poor spring weather in 2012, but this year I have found over 170 adults. It is great to see how quickly the bees and their nest parasites have bounced back following much more favourable conditions last year.