A new buzz in the garden

A squadron of males in pursuit of a foraging female of Anthophora plumipes

It is very frustrating to try and photograph Anthophora plumipes males. These solitary bees fly very fast, with a characteristic high-pitched buzz, and briefly hover to inspect something, before darting to feed for a bit or to check some other clump of flowers, they rarely stop. A. plumipes, or the Hairy-Footed Flower Bee, are one of the first bees of spring. Males appear in mid March a few days before females, and the last individuals seen at the end of May. These bees are sexually dimorphic. Males are brown, large and furry, with middle legs bordered with long feathery flecks of hair (see possible purpose here). Females are a bit bigger than males, but jet black, with reddish pollen baskets. They look like a miniature all-black bumblebee. As bumblebees and honey bees, their ability to maintain a higher body temperatures than their surroundings allows them to fly early in the year: they are effectively 'warm blooded' insects. A. plumipes has a very long tongue and feed in deep flowers. Today I saw the first male of the year, feeding on the first open flowers of Grape Hyacinth (Muscari) in the garden. Later in the day, a couple of other males on Rosemary and Pulmonaria, which have also just started to bloom.

Female A. plumipes feeding on rosemary

Females spend more time feeding than males, hovering in front of the flowers and taking a little time to extend their huge tongue just before, so they are a bit easier to observe and photograph. With the female's appearance, the battle of the sexes begins. Males patrol their territories chasing males and checking flowers for females, even inspecting any passing black object. Males try to mate with feeding females, no preliminaries and no courtship, sometimes several males flying together squadron-like while checking females.

 Once mated, females start making waterproof cells in nearby walls or on the ground, laying eggs and provisioning them with nectar and pollen. But they also have to spend a lot of their time fending eager males off. A fascinating piece of research carried out by Graham Stone in Oxford showed that females harassed by males tend to feed in sheltered flowers to try and avoid them and this has a negative effect in their nectar provisioning, as these flowers take more time to reach. When the local males were removed, females changed their foraging to the outer flowers, when males were returned, females retreated to foraging in the shade. But the poor females are not only harassed by males, a species of cuckoo bee, Melecta albifrons, parasitises them, and they wait outside their nests until the females go foraging to lay their own eggs inside!

Your majesties are back

I had a walk through Pearson Park Wildlife Garden in the afternoon. It was sunny and mild and I was hoping to see the first butterfly, or 7-spot ladybird of the year. There is a lovely flowering heather struggling amongst the fence posts and I checked it. Two beautiful, fresh looking Bombus terrestris queens were lazily feeding on it, accompanied by a drone fly. Note the tawny end of their abdomens, which identifies them as queens. This large heather must be such a priced source of nectar and pollen at this time of year. I will be more fastidious this year recording the flowers on which I find each bumblebee species and write a blog with my results. Bumblebee watching is one of my favourite activities in the summer with my large lavender hedge and nectar-laden Hebe always humming with them. I have recorded all six common species, at least a cuckoo bumblebee and the new arrival Bombus hypnorum in my relatively small garden.

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queen number 1

queen number 2

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