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Citizen Science

How far will Bee No.2 get?

München, 09/18/2017

LMU biologists are using marked bees to determine the sizes of their foraging ranges, with the ultimate goal of helping to protect acutely endangered species. Munich’s human inhabitants can help them find the answers.

Numbered bees can be individually identified, enabling their ranges to be estimated.

Gallery: 1 2 3 4

Number 2 has just set off on a foraging flight over her territory, which includes a flower bed in the western sector of Munich’s Botanical Garden. The forget-me-nots that grow here are beginning to look the worse for wear, as indicated by the brownish tints that mar their blue color. Number 2 is a male specimen of the solitary bee species Osmia adunca. This species was only recently discovered in Britain, and given the vernacular name ‘viper’s bugloss mason bee’ (a more-or-less direct rendering of the German ‘glänzende Natterkopf-Mauerbiene’). Like many other species of solitary bees in Europe, it is regarded as endangered in Germany, and this in turn explains why biologist Michaela Hofmann (26), who has just marked No.2, is interested in its ecology.

Hofmann (26) is working on her PhD thesis at LMU’s Rachel Carson Center. In collaboration with biologists who look after the Bavarian State Collection for Botany, she wants to ascertain the sizes of the foraging territories used by various species of solitary bees in their search for nesting sites, pollen and mating partners. Like ornithologists who ring birds, she marks and releases individual bees so that they can identified on sight. On the basis of sighting reports, she can then estimate the sizes of the bees’ home ranges and document their foraging strategies. Pedestrians who come across any of the marked bees are asked to contact Michaela (see e-mail address below), giving the location and the number (and if possible, a photo) of the bee. The ultimate goal of the project is to ensure the survival of wild bee populations by providing so-called flower strips throughout the city which provide protected species with optimally distributed food sources. The use of flower strips thus promises to enhance the levels of both faunal and floral diversity in the urban environment.

Bee No.2’s territory lies adjacent to the attractive ‘residential development’ that Hoffmann and her colleagues have provided for the local bee population. The wooden structure looks like a set of bookshelves, except that these shelves are laden with pieces of dead wood with neatly drilled cavities, aerated bricks and piles of wooden sticks. The many nooks and crannies available can be used as nesting sites in which the bees can lay their eggs, while a net of fine gauze protects the whole structure from the beaks of hungry birds.

Unlike the honeybee with its busy hives presided over by a queen, wild bees are solitary and live only for a few weeks. The females are responsible for nest-building, egg-laying and pollination, while the male’s sole task is mating. Because wild bees do not form colonies, they do not produce honey, which social bees use as food to tide them over the winter. For this reason, solitary bees were long thought to be of little or no economic importance. Now we know better.

Dexterity required
Its head and thorax are furry and reddish brown in color, the abdomen displays the typical yellow and black stripes, and Bee No.2 now proceeds on another sortie. Its number is inscribed on a red dot about the size of a pinhead, carefully placed on its chitin exoskeleton between the head and wings. In the weeks between late March and mid-May, Hofmann (with the help of biology students) marked some 400 specimens of Osmia cornuta (the Japanese hornface mason bee), which is among the first species of solitary bee to hatch in early spring. Now her attention has turned to the species O. adunca, to which Bee No.2 belongs.

“There’s another one – over there on the right,” she calls out to the two students who are helping her to mark the bees today. While the students are still trying to locate the newcomer, Hofmann has already determined its sex: “It’s a male,” she says. One of students sets out to capture it in a big white net, with Hofmann’s guidance: “Now’s your chance – keep the net closed – you’ve got it, that’s great.” The hunters then take their morning’s catch to the nearby pavilion, where the tools they need for marking are kept. Sheets of paper arrayed with adhesive colored dots, a small bottle of shellac and a fine metal tip to place and attach the marker (a miniature radio transmitter would impede the bee’s movements and reduce their normal radius of action). Hofmann carefully picks up the male between thumb and index finger. Females must be fixed in a foam cushion inserted in a plastic tube in order to immobilize the sting. Marking males only requires a little dexterity and, within a minute or so, the job’s done and the bee is on its way again.

Hofmann’s work focuses on the species O. cornuta and O. adunca because both build their nests above ground and are therefore easier to find, the space between their wings is large enough to accommodate the marking, and many of them haunt the flowerbeds and grassy areas in the Botanic Garden. Indeed, over 100 species of solitary bees have been identified in the Garden, and a total of 570 species have been cataloged in Germany as a whole. Together with honeybees and bumblebees, solitary bees are responsible for pollinating virtually all economically useful plants. The German Association for Conservation and the Environment (BUND) estimates the commercial value of the pollination services provided by insects in Europe as being in excess of 14 billion euros per year, and many plant species – such as bellflowers and tomatoes – are pollinated exclusively by solitary bees. However, just like honeybees, they now have to cope with the ecological changes brought about by modern agriculture, which is dominated by monocultures and meadows that are frequently mown. The wild flowers upon which bees depend have largely disappeared from these landscapes, and it is increasingly difficult for bees to find suitable habitats with adequate food supplies. These difficulties are exacerbated by the depredations of pests such as the mites of the genus Varroa and the deleterious effects of neonicotinoid weed-killers. The EU is currently deliberating whether or not to enact a total ban on the use of neonicotinoids in the interests of bee conservation. According to Michaela Hofmann, solitary bees also labor under yet another disadvantage: They need to warm up in the morning before they can begin to forage – unlike honeybees, which spend the night in their centrally heated hives and can get to work bright and early.

The BUND estimates that more than half of the wild bee species found in Germany are threatened with extinction, while protection measures have tended to concentrate on honeybees. However, the significance of solitary bees for agriculture and the health of the natural environment is slowly being recognized. “In fact, there is quite of bit of hype with respect to solitary bees at the moment,” says Michaela Hofmann – and she hopes that “the tremendous increase in public awareness of their ecological importance” will be beneficial for her research. Visitors to the Botanic Garden or people who live in the neighborhood who happen to discover marked bees and communicate their finds to Hofmann make a material contribution to her study of the bees’ foraging habits. For the success of her project is crucially dependent on this type of citizen science. Even with the help of two students, it would otherwise be impossible to collect sufficient data to answer the questions she is interested in.

She has received almost 50 reports of sightings of the first species she marked, many of them accompanied by photographic evidence. “One man actually found 30 of them,” she says. This is partly because O. cornuta is apparently a stick-in-the-mud. Only one of these bees is known to have left the confines of the Botanic Garden. It was sighted by a 14-year-old boy – all of 300 meters from its site of release. How far will Osmia adunca get?

If you come across one Michaela Hofmann’s marked bees, please get in touch with her at