Paul writes: there are several hoverflies which mimic bumblebees, Volucella bombylans is the most common and widespread. It is also probably the cleverest, as it comes in several colour forms to enable it to mimic a number of different species. This one, with its yellow and white markings, goes with the white-tailed bumblebees, whilst another common form is black with a red tail, to go with the red-tailed species.
From a distance they are good mimics but once you get to know them, or see them close up, they are quite different. They lack the bumblebees’ industrious behaviour of constantly flitting between flowers, instead they are quite happy to leaf bathe. Also, the single pair of wings with black markings and feathery antennae are obvious differences.
The female hoverfly uses her likeness to enter a bumblebee nest and lay her eggs. The larvae then feed on debris in the nest and don’t appear to harm the bees themselves. I usually see them from early May, generally anywhere bumblebees are seen, they last throughout the summer. Often the different colour forms can be found in the same area of vegetation. This one was seen in mid June, on the South Downs in East Sussex.