Bumblebees!

The first bumblebee of the year stumbled across my path today. It was close to a large clump of flowering Mahonia, but on the footpath, so I moved it to the flowers. It was a white-tailed queen bumblebee, Bombus lucorum. Recent bumblebee records from the BWARS (Bees Wasps and Ants Recording Society) site indicated that, instead of overwintering queens, there are now overwintering colonies -mainly of the Buff-tailed, Bombus terrestris but also Bombus pratorum, so that workers can be seen foraging in the winter. As far as I know this has not happened in Northern England yet, so the first bumblebees of the year are sleepy-looking queens in search of nectar and a nesting site. It was sunny and quite warm in the morning, so this bumblebee was awaken and came across this patch of flowers. I guess in the countryside must be quite tricky to find nectar this time of year, with gorse, snowdrops, lesser celandines and few other plants in bloom. Cities and their parks and gardens have much more in offer, rosemary, Mahonia, heathers, Hebe and many other mid-winter flowering plants, and I wonder if this - combined with milder winters - has something to do with this change in reproductive strategies. It would be interesting to test this comparing the  strategies of countryside versus urban bumblebees.

Deceitful drone-flies

Drone-fly

Honey bee

Today we had a beautiful springy afternoon, a brief respite in this cold winter. I saw a drone-fly, Eristalis tenax, feeding on a clump of snowdrops. Drone-flies are a textbook example of Batesian mimicry: a harmless species resembling a stinging one so that predators are deceived and avoid it. Adult drone-flies are hover-flies that resemble honeybees in color, size and even in their flight behaviour. As adults they also feed on flowers - even the same species - making the similarity very precise. But, is there any evidence that predators actually avoid drone-flies mistaking them for bees? In a clever experiment Golding and colleagues actually investigated this using humans - biology university students and schoolchildren. They tested how good they were telling bees, bumblebees and wasps apart, and from their mimic hover-flies using picture plates and questionnaires. Their results show that humans were generally bad taxonomists, as half of the students could not identify a bee, even when they were biology students!. However, the study concluded that more people thought that the mimics would sting than control flies (not resembling bees, wasps or bumblebees), but fewer people thought the mimics would sting than the actual hymenopteran models. This shows that the mimicry works although is not completely effective. An interesting result was that students who had been previously stung were better at identifying the hymenopterans as stinging and were better at telling wasps, bees and bumblebees apart, indicating that experience is an important factor. The study provides the first experimental evidence that mimicry in drone-flies is effective and might help them avoid predation, not only by humans trying to swat or spray them, but by their natural bird predators.
 The students in the previous study were asked to look at small photos of flies and bees for a short period of time, just like any predator who has just seconds to decide if to snatch the insect or let it go. A close up examination of the drone-fly however, easily reveals its nature. Its antennae are quite short compared with the honey-bee, it has got a single pair of wings and typical large fly eyes, also, it lacks polled baskets on the rear legs.

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!