Winners of climate change?

The words 'climate change' tend to have negative, almost apocalyptic, connotations, we struggle to think on its positive effects (unless you live in the UK and you dream on Mediterranean weather to come, of course). Some species, however, thrive on warmer termeratures, so we could expect their distributions to be climate-limited and to increase their range north with increasing temperatures. This is true for many butterflies in the UK. In the first half of the twentieth century, many butterflies were restricted to the southern corner of the UK, whereas nowadays some are steadidly expanding into the north. Expanding butterflies include charismatic garden species such as the Comma, Polygonia c-album, the Speckled Wood, Pararge aegeria and the Holly Blue, Celastrina argiolus. Before the eighties they were absent from East Yorkshire and in the nineties these species become common north of the Humber. All good then? No, there is a problem: for a species to expand its range, suitable habitat needs to be present nearby - within the usual flying range of the species. Throughout the last century, with agriculture intensification, there was widespread loss of wild habitats in the UK. The combined effect of climate change and habitat loss was investigated in depth in a paper by Warren and co-workers. They used a dataset of 46 non-migrating butterfly species with northermost European ranges within the UK and detailed distribution records compiled in the last 40 years. Although all these species seem to develop faster and have denser populations in warmer temperatures (within UK limits) only a quarter of the species actually increased their range as predicted. Species increasing their range tended to be mobile habitat generalists: the species that are more likely to use gardens and other human-related habitats. Most habitat specialists, which tend to be more sedentary declined. This study illustrates the interplay of climate change and habitat availability: in our highly fragmented landscape, generalist, highly mobile species will be the winners of climate change, and we should be able to enjoy them more widely in our northern gardens, but biodiversity as a whole will, sadly, decline.

Comma

Speckled Wood

Holly Blue

Ringlet

Reference

Warren MS, Hill JK, Thomas JA, Asher J, Fox R, Huntley B, Roy DB, Telfer MG, Jeffcoate S, Harding P, Jeffcoate G, Willis SG, Greatorex-Davies JN, Moss D, & Thomas CD (2001). Rapid responses of British butterflies to opposing forces of climate and habitat change. Nature, 414 (6859), 65-9 PMID: 11689943

Alien Invaders

Today I saw the first Harlequin ladybirds of the year. Two individuals adjusting their position in a railing to catch the winter sun. In September 2006, I came across a beautiful, but strange, ladybird. Yellow, large and with 21 spots, I had never seen anything like it, and it wasn't in the insect guide I checked at home. A few weeks later, I found a large black ladybird with black spots. I had a little plastic container with me and took the insect home to photograph it. This time I took a bit more time to identify it. It was a Harlequin, a non-native ladybird species that since 2004 it has rapidly spread across the UK. The Harlequin is native from Asia, and has been widely used as pest control in greenhouses, from where it has escaped. The species had spread invasively in the USA and mainland Europe, from where it invaded the UK.
 This ladybird is unique in that it shows a large variation in color patterns between individuals. The following photos, all taken in Hull, illustrate this.

There was already a very well organized survey to follow the spread of this species in the UK, the Harlequin Ladybird Survey, and I reported these sightings. Data sent by members of the public (in the form of records and photographs) have helped to follow this invasion in great detail. This series of maps from the survey's website show the spread of the Harlequin in the UK year on year.
There is lots of info from the website, not only on the Harlequin, but also on the native ladybirds. You should be able to identify not only the adult ladybird, but also the larva. Here you can compare it with a 7-spot larvae.

Harlequin ladybird larva (with two lines of reddish spiky tufts on top of abdomen).

A 7-spot ladybird larvae (only black tufts on top of abdomen). Tufts are not obviously spiky.

Should we be concerned? Despite the Harlequin being a quite handsome bug, there are fears its explosive spread could result in threats for other ladybird species, either directly or indirectly. They are reportedly very aggressive toward other ladybirds and even humans! Although I must say I have often collected them by hand and they seem not to be aggressive when being handled carefully, in the same way the 7-spot. They eat larvae and eggs of ladybirds if aphids become scarce. Their populations might not be kept in check by predators and parasites. Also, they hibernate in houses in a communal way and they can become a nuisance.

 In Hull, the Harlequin became very common in 2007, but didn't see many in summer 2008, maybe the gloomy, wet summer didn't suit them!

Signs of spring

Once the Chistmas holidays are gone, no matter how cold or gloomy it is out there, it feels so different. The long darkening days of the Autumn are finally gone, and daylight seem to tangibly increase day by day. Sunny, crisp, cold days are a bonus. But is not only the light - or is not only me who feels it - buds are fattening, catkins unfurling and the woodland floor flowers are hurrying up before tree leaves shade the ground. Birds have noticed the longer daylight hours and are singing and pairing. The last day of January and I have already heard wrens, dunnocks, woodpigeons, greenfinches, goldfinches, collared doves, robins and song thrushes singing. It's not only me, is not wistful thinking. There are sings of the new spring already coming.

 Ok, this is BugBlog, where are they? It feels a bit lonely in the sole company of occasional bluebottle or cloud of winter gnats. I am hopeful and keep watch. Any day now, and this means, possible during February, a butterfly, a red admiral, or a small tortoiseshell, will wake up from hibernation and will make my day...

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.

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.