Thursday, 23 October 2008

City butterflies: the Comma

11 September 2006, comma basking on clematis
I have recorded 18 species of butterflies since 2003 in the city of Hull. Four of these I see occasionally, or I have seen just once (White Letter Hairstreak, Brimstone, Orange Tip or Small Copper), species that are more at ease in the countryside. This leaves 14 species that are common enough in the city streets, parks and gardens. One of the most obvious October butterflies is the Comma, Polygonia c-album. This species is recognized by their bright orange background with dark marks and an unique ragged edge-looking wings. Its underside is quite dark in the overwintering generation, with a clear white 'c' in the hind wing: once it closes its wings, it looks like a withered old leaf. Its legs have elegant white stockings. I find the comma difficult to tell apart in flight from the Small Tortoiseshell.
10th October 2008, Comma basking on apple tree
 There are not many sources of nectar around in October; I have recorded commas feeding on Ivy, Buddleia and Cherry Laurel this autumn. In her treasure trove Butterfly Garden webpage, the late Linda Walls also cites Verbena, which flowers in October. The butterflies around this month are the overintering generation. They still fly on sunny days on the look out for nectar sources in preparation for winter. Although the odd individual interrupts overwintering on sunny winter days, they should wake up again at the end of March, ready to mate and lay their eggs.
25th September 2008, Comma feeding on cherry laurel 
The photos above show individuals from the overwintering generation. The one below is the only one I've got from a summer generation ('hutchinsoni'), taken on 8/07/07. Note that its underwings are much paler than the overwintering form.

The following graph shows my sightings for a OS grid square in Hull. it shows the butterfly overwinters from October to late March - frost season here - and the hibernating generation mates and dies off during april. No adults are seen in May and June, but the 'hutchinsoni' or summer generation emerges lays eggs and dies off in July. Finally, September sees a new generation of commas, which are non-reproducing and will overwinter.

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.