Thursday 2 October 2008

The hoverfly hunting machine: watch digger wasps from your garden bench

In 2003, quite a warm summer, an interesting wasp kept watch of the cloud of hoverflies (mainly Episyrphus balteatus) on the nearby flowering Hebe bush from my garden bench. It was there every day and I called it 'Benchy'. A browse in the Chinery guide - the 'Bible' for insects in the UK - showed it was a wasp of the family Sphecidae - a digger wasp. Digger wasps are hunters specialising on various insects, which they paralise and stock on nests to feed their larvae. They excavate their nests, often on the ground, and thats why they are called digger wasps. Wild About Britain provided the ID for the genus, Ectemnius, and even a few guesses for the species ID: E. cavifrons, E. cephalotes and E. sexcinctus, with the first two being the most common. The wasp has returned year after year and I have managed to assemble a collection of photos illustrating a few aspects of the natural history of this fascinating animal.The wasp is yellow and black, with a big head and very large eyes, which make a large area of the head - a very different feel from a common wasp. It is indeed a highly visual animal and it nervously scans around in search for its favourite prey. Oher species of the genus like to hunt other types of flies but Ectemnius cavifrons favours hoverflies.
 When a potential prey is detected, the wasp hovers like its prey, staying stationary at around 10-20 cm from the fly. You need to be quick to manage to focus it, as the wasp is wary of anything large approaching it. The prey is then attacked swiftly, and if the capture is successful, the fly is taken to the nest.
I managed to shoot a hovering Ectemnius wasp, unfortunately a blue plastic car ended up being the background, doh!
For a few years 'the nest' seemed to be located far away from my garden as the wasp disappeared into the distance carrying its booty. But last summer I got lucky and I managed to locate a nest in a dry log in the pile of wood under the BBQ.

Ectemnius wasp about to leave its nest hole.


Jane Adams said...

Brilliant "hovering" picture. My camera just won't focus on stuff like that... Interesting info on the digger wasp as well. I'm in contact with BWARS - if you haven't already looked at it, their website has some really interesting stuff. Jane

Africa Gomez said...

Hi Jane, I use a Canon Powershot G6, I've had it for over three years now and I am so happy with it, I was thinking of upgrading for Christmas though to the Powershot G10. If you are interested in macro, this is a super non-SLR camera. Forget about photographing birds though!

dormousey1 said...

Many thanks for this blog. I too am fascinated by all the critters in my garden and saw something like this grab a fly and fly off with it. It was too fast to get my camera out, but your description, plus a photograph confirming I had these hanging around has helped me identify it.