Bee Quest

by Dave Goulson

  Over the next few days we hiked up and down the mountains, collecting a raft of records of the numbers of different species, and of the flowers they were feeding upon. The species we had never seen before included Bombus wurflenii, a handsome beast resembling the much more familiar red-tailed bumblebee, but with longer, shaggier fur to help it keep warm in these high mountains, slightly brighter markings, and a penchant for larceny which led us to christen it the ‘red-tailed robber bee’.fn5 The monkshood flowers have evolved to be pollinated by long-tongued bees, with their nectar hidden at the end of a long, curved tube, but the red-tailed robber bees unceremoniously bit a hole in the side of the flower using their especially sharp, toothed mandibles, and stole the nectar. There was also the ‘Pyrenean bumblebee’ (Bombus pyrenaeus), an endearingly pretty little bumblebee, resembling its close cousin which we know in the UK as the early bumblebee, but again with a very fluffy, long coat and more yellow. This is a high-mountain species, as you might guess from the name, and it absolutely loved the willowherbs. We also saw a few Bombus veteranus, the ‘old carder bumblebee’, a brownish bee quite similar to our common carder, but with a dusky, smoked colouration.

  Conspicuously absent from the fauna were the rare British species that I had hoped to find out more about – there were no shrill carders or ruderal bumblebees, for example, though I knew that they ought to be in southern Poland. This wasn’t really surprising – we were in the high mountains, and so were mainly finding alpine specialists, not species that one would expect to see in Britain. These high-mountain meadows were beautiful, but they didn’t provide the window on the past that I had hoped for. So, after a few days of trekking up and down the steep slopes of the Tatras, we decided to head elsewhere.

  We had no particular basis on which to make a decision as to where to go next, so we arbitrarily set off from Zakopane in a north-easterly direction. It was initially a bit of a drizzly morning, and our route took us through rolling countryside, the land divided into long, thin fields, many of them only twenty metres or so wide and perhaps one or two hundred metres long, separated by grassy strips. This was nothing like farming in the UK – a tractor wouldn’t even be able to turn around in many of these fields. Or, at least, it was nothing like modern farming in the UK – this was more like the medieval system of open-field farming, whereby the fields belonging to the local lord were divided into numerous strips, with each serf allocated a handful of strips to cultivate. Over centuries the movement of soil when ploughing these strips created furrows between them, and the ridges and furrows can still occasionally be seen in some British fields that have never been ploughed with modern machinery. We stopped and mooched around a bit, but the damp weather was keeping the bees at bay. However, the habitat looked promising – many of the strips were fallow, while others had been sown with clover leys,fn6 red clover, a mixture of red, white and zigzag clovers, or sainfoin. Fallows and clover leys are both now very rare in modern farming, but were a part of crop rotations for hundreds of years before cheap artificial fertilisers became available and enabled farmers to grow arable crops every year, without ever resting the land.

  A little later in the morning we passed through the depressingly drab town of Nowy Targ, which appeared to consist entirely of blocky, weather-stained concrete buildings from the communist era. Shortly afterwards we found ourselves on the southern edge of a range of low, rounded mountains, much less dramatic than the Tatras. These were the Gorce Mountains, a range barely mentioned in our guidebook, which briefly but intriguingly described them as a wild place where wolves, lynx and bears were to be found. The book didn’t mention bumblebees – sadly, the bee section in most travel guides is woefully inadequate – but we figured that somewhere that was good for bears must surely be good for bees. By this time the sun was burning through a little so we pulled over, parking by a bridge over a bubbling stream that flowed south from the mountains.

  We were not in the mountains proper, but in an area of rustic wooden farmhouses, with strip fields and small orchards, the latter mostly planted with old, gnarled apple trees crusted in lichens, proper full-sized trees rather than those with dwarfing rootstocks grown in modern orchards. It really was as if we had gone back in time one hundred years or more. Two aged men were cutting a wheat crop with scythes, then deftly stooking the cut crop by hand (stacking the stems into pyramidal mounds with the grain at the top) to allow the grain to dry and mature before threshing. I had never seen this before – it is a practice that probably went on for the best part of 10,000 years until modern machinery was invented with the intention of making such back-breaking work a thing of the past. Nearby, a woman was cutting fodder from the road verge with a sickle and using her apron as a bag to carry it, presumably back to some livestock. As I watched her, a cheerful-looking young guy called out a greeting to us as he trotted past on a horse-drawn cart laden with marrows, the pneumatic tyres on the cart the only slight concession to modernity. He stared curiously at our butterfly nets and other paraphernalia, so I mimed catching a bee, which probably only served to increase his bafflement. It clearly amused him anyhow.

  We headed off in different directions in search of bees. The higgledy-piggledy nature of the landscape, where everything was done on a small scale, meant that there were lots of edges and forgotten corners where flowers could grow: ‘waste places’, as my flower guide describes them, though in my view they are far from being a waste. The crops themselves often contained flowering arable weeds – familiar species such as cornflowers, fumitory and poppies, and others I had never seen such as large-flowered hemp nettle, a splendid herb with yellow and purple tubular flowers that long-tongued bees clearly adored. It was evident that herbicides were not much used here. These same arable weeds also thrived in the fallow fields, just as they do on the crofts of the Outer Hebrides. As we had seen earlier, some of the field strips were sown with red clover leys, and they were a-humming with bees. Between the field strips, beneath the orchard trees and along the road and track verges, communities of perennial wildflowers had developed: knapweeds, woundworts, cat’s ear, clovers, scabious, marjoram and thyme, along with wood cow-wheat, a most unusual plant in which the young leaves are vivid purple, which together with the yellow and red flowers creates a most exotic appearance. The banks of the stream were rife with the pendant pink blooms of Himalayan balsam, an invasive weed but much loved by bees.fn7 Whichever way one turned, there were patches of flowers and the buzz of insect life.

  In the clover leys there were garden bumblebees, alongside ruderal, great yellow and shrill carder bumblebees. In an orchard I found red-shanked carders, buff-tails, red-tails and tree bumblebees. Along the track verges were common carders, along with old carders and early bumblebees. There were other species too, once again some that I did not immediately recognise – bees that were entirely black with white tails, or black but with yellow tufts near the base of their legs, and still others with distinctive yellow stripes and white or orange tails. Most of the species that I couldn’t identify were males, and I caught a selection for closer scrutiny. When we rendezvoused back at the car an hour later, between us we had recorded fifteen species of bumblebee that we could put a name to, plus what appeared to be several others. So that we could be consistent when we saw them again, we agreed on names for each of the bees that we couldn’t identify – the black bees with white tails became, rather unimaginatively, ‘black white-tails’, and the ones with yellow tufts around the base of their legs became ‘yellow armpit bees’. This may not sound very scientific, but it was the best we could do at the time.

  We headed on into the Gorce Mountains, following a single-track road that wound along a long river valley. We stopped and searched for bees every few kilometres, spending an hour at each place, counting the numbers of each species and recording the flowers they were on, just as I had on Salisbury Plain. I have rarely explored anywhere so idyllic.

  That evening we compared notes, and over some delicious and exceedingly cheap Tyskie beer, Gi
llian and I attempted to work out what all the different species were. As is often the case in entomology, in the end it all comes down to the genitals. I spent about six months during my PhD staring down a microscope at the genitalia of butterflies. Many species of insect can only reliably be distinguished by staring very hard at the male genitalia, which are usually of a unique and often bizarrely complex shape in each species. The female genitals tend to be of little help, but fortunately it was August and males were plentiful. We had no microscope, only a hand lens, and it was tricky, fiddly work trying to get a clear view of such tiny organs by the light of a dim lamp. The beer probably didn’t help in this respect either.

  Eventually we managed to sketch diagrams of the various species we had, and could then compare them to photographs I had brought with us of the genitals of all of the European species (so far as I know there is no law against smuggling bee porn across international borders, at least within the EU). We were in for a bit of a surprise. Gillian, a very pretty, quiet girl, who turned out to be the brains of the party, was the first to spot that all of the odd-looking males that we did not recognise were more or less identical in the tackle department, and their genitalia appeared to match perfectly the photograph I had of the genitalia of the broken-banded bumblebee. I had only ever seen this species on Salisbury Plain, and there all the males were very similar – and closely resembling buff-tailed bumblebees, with two yellow bands and a whitish tail. In Poland, it seemed that the males of this species had gone berserk, adopting a bewildering and rather attractive array of colour patterns. This is unexpected in bumblebees, for their coloured stripes are thought to have evolved as warning colours to signal that they have a sting, and hence keep predatory birds at bay (though great tits and bee-eaters wolf them down regardless). What is more, it has been suggested that the reason many species look so similar is that they mimic one another – by all adopting the same colour patterns, they collectively send a stronger signal to their predators.fn8 Male bumblebees don’t have a sting (which evolved from the egg-laying tube, which of course males don’t have) and so I presume that their coloured stripes are a bluff. By resembling the females, they may benefit by association – birds having learned earlier in the year from experience with the queens and workers that creatures with this colour pattern are dangerous.fn9 One might therefore expect the males to look very like the workers, but in many species they do not. Usually they are a little more brightly coloured, often with broader yellow bands and fluffy yellow faces. This would seem to be a foolish strategy so far as the risk posed by predators is concerned, but is presumably the result of sexual selection – perhaps the virgin queens prefer brightly coloured males, and so they have to have bright colours to stand any chance of mating. Having sex and then being eaten is a success, in evolutionary terms, compared to living a long life without either. I must confess that this is all wild speculation – I have no evidence whatsoever that queen bees are attracted to brightly coloured males, but it happens in butterflies and birds, so why not bees? Actually, I did once have a Bangladeshi postdoc who studied mating choices in bumblebees and found that females were more likely to mate with the males with the longest legs, but that is another story.

  Anyway, to cut to the chase, it is very hard to explain why male broken-banded bumblebees in Poland are so variable in colour. One might expect them to be brightly coloured to impress a mate, or to copy the colours of the females to avoid getting eaten, but adopting wildly varying patterns makes no sense. Perhaps Polish females have eclectic tastes, or prefer to mate with unusual-looking males, which might favour the proliferation of colour forms. It would make a fun research project to investigate further.

  At least now we were able to identify the different species that we found, and could set about collecting lots of data on the various types of bumblebee in the area. We settled in a hotel in Ochotnica Gorna, a picturesque village which straggles along the south bank of the Ochotnica River in the heart of the mountains. How the hotel could possibly make a living was unclear as it was almost empty in the height of the summer season. There seemed to be very few tourists here compared to the Tatras, and no overzealous traffic policemen, which suited us just fine.

  We spent the next week exploring the rolling mountains and valleys in search of bees. Along the river valleys were strings of small farms, all with tiny fields, and minimal signs of farm machinery. Some farmers had small tractors, but there was no space for the huge combine harvesters that we see in the UK and so almost all of the harvesting was still done by hand, while horse-pulled carts seemed to be the most common form of transport. Higher up, the farmland gave way to pastures, grazed by small herds of cattle and sheep, and higher still were areas of dense forests interspersed with heathland. It was bilberry season, and we encountered many locals out collecting buckets full of the small purple fruits, some armed with odd contraptions consisting of an array of parallel metal blades fitted to a glove, with which they combed the berries from the bushes. When I first saw a guy emerging from the bushes, dark juice dripping from the spray of blades attached to his hand, my heart skipped a beat as I recalled the Freddy Krueger character from the horror film A Nightmare on Elm Street.

  We didn’t encounter any bears or wolves on our travels, sadly, but we did see a host of other wildlife. Butterflies were everywhere – blues, fritillaries, swallowtails, whites and browns – my favourite being the scarce copper which abounded in the mountain meadows, their red-gold metallic wings gleaming in the sunshine. The bumblebee-mimicking hoverfly Vollucella bombylans was common, wonderfully furry flies that come in a range of different colour morphs, each copying the patterns of a particular bumble-bee species. I saw my first wart-biter cricket – a huge and beautifully camouflaged emerald-green and black beast which lurked amongst the tussocky grass on south-facing slopes. In the UK this species occurs at just three sites in the South Downs near Brighton, but in the Gorce Mountains it seemed quite common. They have fearsome mandibles, from which they derive their name – in days gone by, it is claimed that they were used in Sweden to bite off warts, though it would seem to me that there must be easier ways of doing this. We didn’t find many more bumblebee species to add to the tally from our first day – a handful of cuckoo bumblebees, including one new one for me, Bombus quadricolor (the ‘four-coloured cuckoo bumblebee’?), which specialises in attacking the nests of the broken-banded bumblebee. What we did find were a great many of some of the species that are enormously rare in Britain – just as I had hoped. Shrill carders were common everywhere, alongside red-shanked carders, broken-banded and ruderal bumblebees, plus all of the common British species.

  So what did all our data show? Since I began searching for rare bumblebees on Salisbury Plain in 2002, I had been trying to work out why some species have declined precipitously, in some cases going extinct, while others seem to be doing pretty well. This is actually a general question one could apply to most groups of animals or plants. Why are marsh tits less common than blue tits? Why are lady’s slipper orchids close to extinction, while the common spotted orchid remains, as the name suggests, common? If one studies organisms in sufficient detail, one may discover the answer. For example, researchers have found that the Adonis blue butterfly is warmth-loving and can only thrive on close-grazed, south-facing chalk downland and so it is inevitably scarcer than its cousin the chalkhill blue, which is slightly less fussy and can live in shadier, longer turf and north-facing sites. Bumblebees had thus far proved to be more reluctant to give up their ecological secrets.

  Once back from Poland, I spent many hours analysing the huge data set that we had gathered. Crunching data is not everyone’s cup of tea, but it can be surprisingly satisfying, especially when clear patterns emerge. Most of the species that have become rare in the UK had rather similar flower preferences – they tend to be longer-tongued bees, very partial to red clover and other legumes with deep flowers, and also to plants in the mint family such as the hemp nettle. The broken-banded bumblebee was the only e
xception – this is a short-tongued bee, and in Poland it visited a huge range of different flowers. While I was playing around with these data, another of my PhD students, Claire Carvell, showed me her analyses of changes in abundance of flowers visited by bumblebees in the UK between 1930 and 1999. Her studies neatly but depressingly showed that 76 per cent of flower species had declined in the frequency with which they were recorded in survey plots, but that deep flowers seemed to have been particularly hard hit. Red clover had declined by 40 per cent in frequency in just twenty years, from 1978 to 1998. It was hardly surprising, then, that the long-tongued bees, which in Poland were still thriving in the clover leys, have declined in Britain. There is still red clover about, but there is far less of it than there used to be.

  At more or less the same time that Claire and I were comparing notes, two Dutch biologists, David Kleijn and Ivo Raemakers, were trying to tackle the same question, and had hit upon an ingenious idea as to how they might travel back in time to study what bumblebees used to do. Rather than going to Poland, they went to the museum. The Netherlands has a similar history of agricultural intensification to Britain and is also a very crowded country, so its bees show a similar pattern of decline. In fact, exactly the same three species that went extinct in the UK also disappeared from the Netherlands (the apple bumblebee, Cullem’s bumblebee and the short-haired bumblebee), and a near-identical set of species have declined dramatically, including the brown-banded and shrill carders, and the ruderal and broken-banded bumblebees. Europe’s museums are stuffed full of pinned bumblebees, many caught during the great era of amateur insect collecting in the first thirty years of the twentieth century. Klein and Raemakers realised that many of these bees still had pollen in their pollen baskets, pollen that had been sitting there for roughly one hundred years. It is one of those brilliant ideas that seems obvious once you’ve thought of it – by identifying the pollen grains, they could quantify what flowers these bees were visiting all those years ago. They collected and analysed the pollen from the legs of museum bees, not just from the Netherlands but also from Belgium and the UK. They then went back to the same sites where those bees had been caught, and collected fresh pollen from the common species that still lived there (the declining species had gone from the sites, though they cling on elsewhere). Their data confirmed that the species that were subsequently going to decline tended to collect pollen from fewer plant species than those that managed to adapt to the coming changes. They were more specialised – several of them, particularly the long-tongued species, were very dependent on red clover and other legumes. The broken-banded bumblebee seemed to be heavily dependent on harebells, while the heath bumblebee favoured heathers and bilberries. In comparison, the species that coped better with what the twentieth century was to throw at them tended to have more catholic tastes to start with, visiting a broad range of flowers for many different plant families. What is more, they found that the flowers that the declining species preferred had themselves declined more than average during the twentieth century – these bees had been unlucky, happening to prefer plants that weren’t going to do well. Harebells, for example, are now pretty scarce flowers in most places, so any bee foolish enough to have a real taste for them was going to be in for a tough time. This of course was more or less exactly what our own data showed – that our rare species had become rare because their preferred food had become scarcer. In Poland, still rich in flowers of all types, there was room for all of them to thrive. It is always reassuring when studies addressing the same question from completely different angles arrive at more or less the same conclusions.