Tuesday, 30 June 2009

The Leaf-Cutter

A leaf cutter resting: note the scissors!
The other day I was watching Wool Carder bees when another bee landed in a plant next to the Stachys. It was a Leaf-Cutter bee, who proceeded to honour her name and started cutting a circle in a leaf. As I was there, kneeling, ready and close by I took a first shot thinking that I would have time for more. But the next shot was a blur of the bee carrying the leaf away once she curled it under her body! They are so fast cutting as if they had scissors. There are eight leaf-cutter bees in the UK all of the genus Megachile. Unfortunately, identification is not easy from live individuals and this has hampered research into them. I could identify the plant the bee used to cut her circles of leaves as Circaea lutetiana, with the delightful common name of the Enchanters Nightshade. It is a plant that grows on its own accord in the garden, in shady places, that covers the ground and has pretty tiny flowers. After the multiple visits by the leaf-cutter, the plant has now been left in a sorry state. I thought that leaf-cutters preferred roses, but my roses are untouched. Fabre dedicated a chapter of his book Bramble Bees and others to the leaf-cutters. As it is a recurring theme in his book, he marvelled at the ability of the leaf-cutter to cut perfect circles and ellipses of leaves of different sizes depending of their use to build her nests. He also contrasts the instinct of the bees - the use of leaves for nest building -  with the plasticity of the actual choice of plant species depending of their properties and availability. Leaf-cutters use existing holes to build nests. Given that my bee posts have now been covered by plant growth and I cannot see what's going on in them we have made a new bee hotel, in the hope that summer bees will be tempted to use it. I'll keep you posted.
The leaf-cutter in action. This female has been kindly identified by Stuart Roberts in WAB as Megachile centuncularis
The bee leaving with her piece of leaf
A brief stop for repositioning the leaf piece
Megachile sp. feeding on Osteospermum, the pollen filled scopa underneath her abdomen is clearly visible. These bees often keep their abdomen lifted up when feeding.
The new bee hotel: vacancies.

Monday, 29 June 2009

Little footprints on petals

I find it difficult not to write about bumblebees these days. We've had a week of showers, and bumblebees do not seem to mind much, going about their business rain or shine. They have the advantage of being warm-blooded insects, they keep their body temperature above the environment, and therefore, they do not need the sun to warm up and forage, like other insects. When the flowering bushes are buzzing, how do bumblebees decide what flowers to visit and when? Do they follow a pattern or do they choose specific flowers? If you watch a single bumblebee visiting a plant, say, a foxglove or a Stachys spike, it is easy to see that they follow a pattern: from the bottom up, and that might suffice to avoid visiting the same flowers twice; but what if there are many bumblebees feeding together? Surely they will end up visit flowers that have just been sucked up dry of nectar? Well, research shows us an unexpected aspect of bumblebee's - and bee's - natural history. Bumblebees actually mark, with scents detectable by other bumblebees, each flower they visit with glands located on their tarsi - at the end of their legs. Some of these marks are repellent, so that bumblebees avoid flowers that themselves - or others - have recently visited and, as the chemicals are volatile, by the time they have faded, the flower is full with nectar again. Interestingly, flower scent marks seem to be recognised not only by bumblebees of the same species, but also by several other bumblebee species, and bees visiting the same flowers, despite being different chemical compositions. Jane Stout and Dave Goulson carried out simple, but labour intensive, experiments by with Bombus lapidarius and Apis mellifera (the honey bee) feeding on a large patch of Melilotus officinalis, showing that both species recognise each other marks on flowers and avoided recently visited flowers. What I found really interesting around this topic is that, in a different study, Gawleta and coworkers showed that bumblebees avoid to a larger extent the flowers previously visited by Anthidium manicatum, the Wool-Carder bee. This could be a response to the aggressive behaviour of males of this territorial bee.
Bombus pascuorum leaving a Stachys flower. Wool-carder bees have been quite late this year and it is the first time I see B. pascuorum feeding on these flowers.
Female Wool-Carder bee feeding on Stachys. Males have not emerged yet and both bumblebees and Wool-Carder bees seem happy to feed together.

Sunday, 21 June 2009

Fork-Tailed Flower Bee

There are not many UK bee species that can be readily identified based on a description. Anthophora furcata must be one of them. A few days ago I observed this bee feeding successively on Lithodora and Teucrium, both favourites of A. plumipes. My description on the day (10th June) was: 
New bee: Osmia rufa size, reddish, chestnut hair all over bee with yellow face and black antenna, long tongue.
I didn't have my camera with me - sometimes, I cannot do gardening and watching at the same time, only sometimes. A bit hopelessly I started a thread in Wild about Britain. In not even three hours after posting, I was surprised by an answer, Eucera (WAB Aculeate expert) suggested Anthophora furcata. After checking a few photos on Flickr, it became clear that this was the bee. Since then, I have spotted A. furcata on a a few occasions, so, it seems that is not a rare bee in Hull. So far, only males. Females are darker and with a reddish-orange 'tail' fringe. The species is present from early June to early August according to the Essex Field Club records - just two months! and specialises on Lamiaceae (mint family). It makes its nests by excavating tunnels in rotter wood. According to an excellent Solitary Bee site by Nigel Jones, the reason why they often go unnoticed is that they might be confused with the bumblebee Bombus pascuorum.
Today, I managed to get a few shots of a male feeding on a lovely patch of lavender, accompanied by Bombus pascuorum and B. terrestris.
A. furcata male, note how high his face is in the Lavender flower, this is due to the size of the tongue, it doesn't need to make an effort.
A different angle of the same male
The following is a shot of Bombus pascuorum for comparison. The yellow face is distinctive of male A. furcata. B. pascuorum always have black faces.

Friday, 19 June 2009

Bumblebee home ranges

Have you ever wondered where do the bumblebees visiting your garden come from? How far do they travel from their nests? How can scientists find this out? It would appear that an obvious strategy would be to mark bumblebee workers from single nests, survey the surroundings of the nest and map where they go. In practice, this proves difficult as it is difficult to find enough marked workers in a reasonable amount of observation time. Another option is to mark bumblebees, release them at increasing distances from their nests and see how well they return home. When this last experiment was performed bumblebees -Bombus terrestris in particular - could return home from the astonishing distance of 9.8 km! However, this does not show how far from their nest they normally forage. In this paper, Mairi Knight and co-workers used an elegant, sophisticated, but cost-effective approach which yielded a lot of data. The premise of their work is that the workers from a nest are expected to be full or half sisters - offspring of the same queen. What they did is to follow a linear transect capturing workers of four common bumblebee species at regular intervals.
The sampling design: across agricultural land, with some woods, hedgerows, and a nearby town in Hertfordshire. The sampling points (in red) are approximately 250 m apart.

They screened the workers using 8 to 9 very variable genetic markers (microsatellites, which are also used in human paternity testing) and identified sisters by assessing the number of markers sisters should be expected to share. Their results were then used to calculate the maximum foraging distances of nestmates of the four species. It was 449 m for B. pascuorum, 758 m for B. terrestris, 450 m for B. lapidarius and 674 m for B. pratorum. Quite a long way, I would say. B. terrestris is the species flying longer to forage, and also the species with the larger workers and more workers per nest. A much more striking result of this study, though, is the number of nests from which workers come to feed in a specific sampling point. Knight and coworkers estimated that, on average, B. lapidarius workers came from 75 different nests to a specific sampling point, these figures were 43 nests for B. pascuorum, 52 for B. terrestris and 37 for B. pratorum. Of course this study applies to farmland, but for B. terrestris, nest densities might be even higher in urban areas. It makes me feel good to know that even when, frustratingly, there are no bumblebee nests in my garden, it still supports a very high number of nests from a range of species.

Tuesday, 16 June 2009

Wool-Carder Bee watching 2: The female

The first time I came across Anthidium manicatum, the Wool-Carder Bee was after hearing it, not the usual humming noise bees make when flying, but that produced by a female's jaws cutting the hairs of a plant I had recently planted in the garden, Lamb's Ears (Stachys byzantina). Since then, this has been a plant that has not been missing from the garden, just because it is a sure way of attracting Wool-Carder bees. The contrast between male and female's behaviour couldn't be more stark. Female wood-carder bees get about their business bothering no other insect, they are even quite shy and easily disturbed. They emerge more or less at the same time than males, sometime in June and set about nesting in some pre-existing cavity. Their cottony nests were described in the early 20th century by the French entomologist, Jean Henri Fabre in his book 'Bramble Bees and Others' as 'by far the most elegant known specimen of entomological nest-building'. Fabre was a curious naturalist, especially fascinated by bee nesting habits and encouraged solitary bees to nest in reed stems and glass tubes so that he could observe them in action.
Fabre described the female carding behaviour in vivid detail:

"Faithful to the plant recognized as yielding good results, the Anthidium arrives and resumes her gleaning on the edges of the parts denuded by earlier harvests. Her mandibles scrape away and pass the tiny fluffs, one by one, to the hind-legs, which hold the pellet pressed against the chest, mix with it the rapidly-increasing store of down and make the whole into a little ball. When this is the size of a pea, it goes back into the mandibles; and the insect flies off, with its bale of cotton in its mouth."
But this striking behaviour had not escaped notice of one of the most observant and meticulous recorder British naturalists in the 18th century, Gilbert White, who wrote in 'The Natural History of Selborne'
Female wool-carder bee scraping the cotton away
She rolls the cotton into a ball
The ball of cotton is now finished
And the bee flies away with it to her nest
This is the Stachys byzantina, still intact today, waiting for the shaving of the bee.

Saturday, 13 June 2009

Wool-Carder Bee watching 1: Male watching

The Wool-Carder Bee (Anthidium manicatum) is one of the most fascinating bees to watch in my garden. They are handsome bees, quite robust, with white-haired legs and brown hair on the body and stark yellow and black markings in the face and abdomen. Unlike most bees, Anthidium males are larger than females. The first Wool-Carder Bees appear in June. The males are territorial and defend a patch of flowers - frequented by females - with constant patrolling, and aggressively chase off or attack any intruders that pretend to 'steal' their nectar and pollen. It has been reported that they have killed other bees or bumblebees or rendered then unable to fly. Males have five pointed spines at the end of their abdomens with which they try and pierce other insects. The resident male flies when in patrol and hovers momentarily facing any possible insect, in most cases, the other bees flee when chased by the resident male. The males are most active in the middle of the day, resting on the early morning and late afternoon, often on a flower, holding on characteristically with his jaws. On this time, the other bees can forage in peace.
Male resting on Lavender
When the male notices a female in his territory he approaches and hovers behind her, waiting until she is feeding to jump on her and mate. Sometimes the male just approaches and seem to touch the female and leave her alone to feed.
Wool-Carder bees copulating on Lavender. In this photo the larger size of the male is obvious
Wool Carder bees have relatively long tongues (7.5-8.5 mm) and like deep flowers such as Lavender, Jerusalem Sage (Phlomis), Woundwort (Stachys), Tree Germander (Teucrium) and Sage (Salvia officinalis). Mating often takes place on these flowers.
Male feeding on Stachys byzantina or Lambs' ear
 Research by Severinghaus and coworkers on American populations has shown that male Wool-Carder bees follow two strategies to secure access to females. Larger males are territorial and mate with females feeding or gathering wool from their patch. Smaller males are 'wanderers' and sneak on resident male territories to mate with foraging females. This research, following marked bees on two summers, uncovered a remarkable level of turnover in territory ownership, with most territory ownerships lasting less than 4 days (the maximum was 30 days).
 In my garden, a male often rested on Jerusalem sage. Possibly the same male that ended up being a meal for a spider that lived on the same plant.
Male resting on Jerusalem Sage flower
Enoplognatha ovata has just captured the male