by Dave Goulson
This is all well and good, but what harm might these friendly, furry beasts be doing? There are a number of possibilities. The most obvious danger was that they might out-compete the native species, for bumblebees, along with all other bees, feed only on nectar and pollen; and as they need a lot of nectar to fuel their activities, this inevitably means less for others. In Tasmania, the native nectar-feeding fauna includes hundreds of small bee species, other insects such as flies, beetles, butterflies and so on, several varieties of parrot, and also ten species of long-billed birds variously called honeyeaters, wattlebirds and spinebills (four of which occur only in Tasmania). If nectar and pollen are plentiful then adding bumblebees into the mix may not matter; but if there is a shortage, any food taken by bumblebees means less food for the locals, quite possibly with disastrous effects if the creature concerned is already suffering from the impacts of logging or introduced predators.
A second possibility is that adding bumblebees to the Tasmanian mix might reduce pollination of native plants. You might be wondering how having bumblebees could reduce pollination – after all, they are very good at the job. Let me give you an example. Honeyeaters specialise in feeding on nectar; they are the Australian equivalent of a hummingbird (although they do not hover), with long, down-curved bills for reaching into deep flowers. Many Australian plants have specifically adapted to such pollination, evolving deep tubular flowers in which only the honeyeaters can reach the nectar. Typically, as the bird probes down it receives a dab of pollen on its forehead, and as it travels on from flower to flower it spreads the pollen, so fertilising the flowers. Now imagine a bumblebee faced with such a flower. Its tongue is not long enough to reach the nectar, but buff-tailed bumblebees are adept at nectar robbery – by biting a hole in the back or side of the flower they can access the nectar, but go nowhere near the reproductive parts, so they do not pick up any pollen, and the flowers do not get fertilised. With lots of bumblebees at work, it is easy to imagine harmful effects on both the honeyeaters and the plants.
A third possibility is that bumblebees might improve pollination of the undesirable alien weeds with which Australia is rife. This is probably the simplest and most likely impact. One of the commonest routes for the introduction of non-native weeds was as seeds in the hay brought over on ships with livestock from Europe, the result being that almost all of the common hayfield plants of Europe now occur in Australia. Many of these weeds are naturally pollinated by bumblebees in their native range. Some of them are welcome in Australia; clover, for example, is a valued food for livestock. But many, such as thistles and gorse, are invasive weeds. Imagine then the likely consequences of introducing a more effective pollinator, one with which these plants evolved for millions of years in Europe. Plants such as gorse have flowers that have adapted to be pollinated by large furry bees. The tiny native Tasmanian bee species might well be quite hopeless at pollinating these flowers. But with bumblebees on the scene, it is possible that these weeds could produce more seeds and spread faster. One might even imagine that there might be ‘sleeper weeds’: non-native plants which have remained rare for decades in Australia because they rely entirely on bumblebees for pollination. Add bumblebees, and these sleeper weeds might awake, rampage and spread.
Was any of this actually happening? We needed more time if we were to get answers, and so it was that in December 1999 I returned to Tasmania with Jane and an extra pair of hands in the form of a second PhD student named Andrea Kells. This time I had managed to negotiate a sabbatical and could stay for the whole of the Antipodean summer if need be.
We had a two-step plan of action. First, we decided to see whether the native bees had become less common in places where bumblebees had arrived, by comparing their numbers at sites within the expanding range of the bumblebee with sites just outside the current range. The second stage focused back on the tree lupins. Lupins are a typical bumblebee-pollinated flower; those in my garden in Southampton seemed to be pollinated solely by bumblebees, and it is said that tree lupins in California are also bumblebee-pollinated. We had also read that tree lupins in New Zealand and Chile are considered to be major weeds (although admittedly rather pretty ones). Tasmania has a similar climate to New Zealand, yet here tree lupins seemed to be generally rather scarce, and that led us to wonder whether the New Zealand lupins had benefited from 100 years or so of bumblebee pollination, whereas those in Tasmania were lacking their main pollinator until very recently. Could it therefore be that Tasmanian tree lupins were a ‘sleeper weed’, and that the bumblebees’ arrival would awaken them to their true weediness potential? The answer lay with finding tree lupins both within and without the current bumblebee range, with the aim of measuring whether they were setting more seed where bumblebees now occurred.
This all required a lot of driving along the quiet and winding Tasmanian roads. Which in turn of course allowed me to indulge my pie obsession as we paused to lunch on delicious seafood pies, filled with luscious juicy scallops from the chilly coastal waters. We also saw many more squashed animals, a few live echidnas and, on one memorable occasion, a stunningly beautiful tiger snake crossing the road, its ebony scales glinting in the sunlight. These snakes are deadly, but I could not resist getting out of the car to have a good look and timidly snap a few pictures. It didn’t seem to be remotely interested in me, and slithered gracefully off into the undergrowth.
To count the numbers of native bees in different places we carried out one-hour timed searches, during which we recorded every bee that we saw, catching those that we didn’t recognise for identification later. We also stuck up a yellow A4-sized ‘sticky trap’ on a tree or telegraph post at each location. These are simply bright yellow plastic sheets covered in phenomenally sticky glue – insects mistake them for enormous rectangular flowers and when they investigate become permanently stuck. After a week we came back to collect the traps. This quickly turned out to be rather scary. Although I have spent virtually my whole life chasing bugs of one sort or another, I have to confess to a bit of an aversion to spiders. I think I picked this up from my mother, who to this day becomes near hysterical at the sight of even the most innocuous spider. Australia is well known for its poisonous snakes and spiders, and amongst the most frightening of them all in appearance is the huntsman. They are not actually poisonous, but they are massive, crab-like, hairy beasts with huge curved fangs and eight eyes glinting with malicious purpose (or at least that is how my fevered imagination remembers them). They move like lightning, and their favourite habitats are the telegraph posts and tree trunks along which they prowl at night in search of their prey. They have flattened bodies for sliding into cracks and gaps under dead bark, and they obviously liked to hide under our sticky traps. Some would also walk over our traps at night and become stuck. The very largest ones were so powerful that they could tear themselves off the glue and escape, leaving a trail of bristles and footprints. All of this made collecting our sticky traps a harrowing and adrenalin-laced business for an arachnophobe. Almost every trap had at least one huntsman stuck to it, or one ready to shoot out from underneath as soon as the trap was moved. Worst of all were the ones where hairy footprints spaced a hand’s width apart showed that a particularly large spider had pulled itself off the glue, and was no doubt lurking somewhere nearby waiting for revenge.
The spiders aside, our bee-counting revealed something we hadn’t anticipated. Just over half of all the bees we counted were honeybees. Honeybees are the anorexic cousins of bumblebees, smaller, slimmer and much less furry; they are usually fawn or tan in colour with vague darkish stripes. Now honeybees are also not native to Tasmania. They come from Europe and the Middle East, but they have been domesticated by man since prehistory (ancient Egyptian hieroglyphs contain carvings of bee hives). Because they have always been highly valued both for crop pollination and for their honey, we have imported honeybees to every country in the world except Antarctica. They were introduced to Australia in 1821, and there is now a very big honey industr
y. Tasmanian leatherwood honey is particularly delicious, and fetches a premium price.12
When we analysed our data, which contained many thousands of records of insects at over 120 sites, we found no measurable effect of bumblebees whatsoever. Places where bumblebees had recently invaded had just as many native bees (both in terms of numbers of different species and numbers of individual bees) as places where bumblebees had not yet arrived. By contrast, the honeybees were having a major effect. Wherever we found honeybees, there were on average only one-third as many native bees. With hindsight, this result is perhaps not surprising. Honeybees were much more numerous than bumblebees, and as they also live in much larger colonies, if any non-native species was going to be competing with native bees by using up lots of pollen and nectar then honeybees were always going to be the more likely candidate. They also have quite short tongues, as do all the native bee species, so they tend to feed on the same flowers, whereas bumblebees have longer tongues and so tend to choose different flowers (although there is lots of overlap). So if bumblebees were impacting on native species, they were far more likely to be doing so on birds such as honeyeaters, who favour deeper flowers.
Discovering that honeybees seemed to be having a harmful effect on native species put us in a rather delicate position. Bumblebees had recently arrived in Tasmania, and had we found that they were causing harm to native bee numbers nobody would have been too upset or surprised. On the other hand, honeybees are highly valued and make a significant contribution to the economy. Many people make their livelihoods from keeping them, and they no doubt contribute to pollination of many crops. Understandably, these folk would not appreciate a bunch of Poms swanning over for a few weeks and then declaring their beloved honeybees to be undesirable aliens. But on the other hand, there is no doubt that honeybees are a non-native species. It also seems to me common sense that flowers can produce only so much nectar, and that there can therefore be only so many bees in a particular habitat. Something has to give, and that thing is likely to be the local flower-visiting insects. This is just as true elsewhere in the world as it is in Tasmania. There are huge honey industries in New Zealand, mainland Australia (I’ve always thought eucalyptus honey tasted rather medicinal but it is very popular), and throughout the Americas, and in all these places honeybees are non-native.
Let me bore you with a few figures. A single honeybee hive contains 50,000 workers or more, and it is common for beekeepers to put twenty hives in a single place – 1 million bees. A single honeybee nest harvests up to 60 kilograms of pollen and 150 kilograms of nectar per year. At high hive densities, honeybees can harvest up to 22,500 kilograms of honey per square kilometre. The New Zealand honey industry produces 8,000 tonnes of honey per year from 227,000 managed hives, or thereabouts. Some of these vast quantities of honey are obtained by the bees foraging on crops which are in turn pollinated, but a large proportion comes from the bees visiting wild flowers. With this much honey being taken by honeybees, it seems obvious that there is likely to be an impact on other creatures that need nectar.
Even in places where honeybees naturally occur such as the UK, beekeepers often create unnaturally high densities. A student of mine, Kate Sparrow, recently found that bumblebees in Scotland tend to be smaller in places where there are lots of honeybees, presumably because of competition for food.
I do not want to pick a fight with beekeepers. Most are very fond of bumblebees and other insects. They are invariably aware of the shortage of flowers in the countryside and keen to support efforts to make it more bee-friendly. In short, in many ways beekeepers are the natural allies of a bumblebee conservationist such as me. But there is no denying the potential conflict and I am sometimes saddened by the strong reaction of some beekeepers to the merest hint that their bees might occasionally do harm. It is the simple truth. In fact, there are rather few places where there is likely to be any major conflict between conservationists and beekeepers. In most of the farmed countryside, be it in Tasmania, New Zealand or the UK, the benefits that honeybees provide through pollinating crops and producing honey greatly outweigh any small impact they might have on other insects. But in a few special places, it might be wise not to station honeybee hives. Imagine a small nature reserve in Tasmania, for instance, supporting the last-known surviving population of the striated dongle bee (a hypothetical creature, in case you were wondering). Would this be a sensible place to put twenty honeybee hives? Similarly, imagine a small Hebridean island called Oronsay, supporting a population of the endangered moss carder bee. Would this be a sensible place to put another twenty honeybee hives? In both cases (one theoretical, one real), the obvious answer would be no. But it is surprising how much hot water I have got into for saying so.
I have digressed. Jane, Andrea and I set out to discover whether bumblebees in Tasmania were doing any harm. So far as native bees were concerned, the answer seemed to be no. We also looked at the seeds of the introduced tree lupins to see whether the arrival of bumblebees had awakened a new sleeper weed. In this respect, bumblebees appeared to be having a strong effect. Lupins are related to peas, and their seeds form in rather similar pods. Each yellow spike has lots of individual flowers attached to a central stem, and if all goes well then each flower produces a pod full of seeds. In places where there were no bumblebees, roughly 60 per cent of flowers fell off without setting any seed, and where they did set seed there were only about two seeds per pod. In contrast, in sites where bumblebees had become common, only 30 per cent of flowers set no seed and on average there were about six seeds per pod. Overall, bumblebees were allowing each lupin plant to produce more than four times as many seeds. It seemed likely that the arrival of bumblebees might well lead to tree lupins becoming as big a weed in Tasmania as they are in New Zealand.
Eleven years later I wanted to find out what had happened. By that time I was based at Stirling University, and an excuse to escape the Scottish winter for some Antipodean sun was even harder to resist than ever. So it was that in December 2010 I found myself reprising our whistle-stop tour of Tasmania, this time with a PhD student named Ellie Rotheray, who was moonlighting from her studies of the UK’s rarest fly, the pine hoverfly.13 On our first morning, with lashings of coffee inside us to counteract the effects of jet lag and a thirty-eight-hour journey, we tried to find some of our former lupin populations just south of Hobart. We hadn’t had the benefit of a GPS back in 1999 so we had no precise coordinates to go to, but I did have scribbled notes on a very tatty map and I thought that I remembered the sites fairly well. The first lupin patch on the edge of the pretty seaside town of Kingston was still there, just, but had largely been destroyed by diggers creating what appeared to be a rough car park. Only a couple of bedraggled plants survived, half-buried under the rubble. The second patch, a little further south along the side of a main road, seemed to have disappeared entirely. We drove up and down looking for it, as I scratched my head and mumbled apologetically, ‘I’m sure it was round here somewhere…’ I was starting to fear that we had flown 11,000 miles on a wild goose chase. We headed south, and as we failed to find a couple more lupin populations, I felt increasingly foolish. It wasn’t until we reaching the sleepy fishing village of Dover, near Tasmania’s southern tip, that we saw our first decent patch of yellow lupins. Dover is a tiny place, a cluster of fibreboard houses strung around a beautiful sandy bay, the sand strewn with abalone shells from the local fishery. At the back of the beaches the lupins had been spreading in the dunes, forming a dense strip for half a mile along the bay. They looked stunning, framing the icy blue sea, surf and sand with a crescent of vivid yellow, but they had been steadily strangling the native flora, forming a dense, impenetrable thicket.
The pattern was similar elsewhere: coastal populations tended to have expanded, while the inland populations tended to be small and ephemeral. Many of the inland populations we had found in 1999 had gone, wiped out by herbicides or development, but other populations had popped up here and there. The worst infestation w
as on Bruny Island, a gorgeously remote and sparsely populated twist of land off the east coast of southern Tasmania, home to more echidnas and fairy penguins than people. Here, the lupins were running amok, spreading along the sandy coast and in dense swathes into the gum forests inland. We dutifully counted every plant in all the lupin patches we could find around Tasmania; as ways to earn a living go, I can think of many worse for it is one of my favourite places on earth, paradise for a naturalist. In our twelve-day tour, as well as lots of lupins we saw pods of dolphins frolicking just feet from the shore, sea eagles, flocks of black cockatoos, penguins, duck-billed platypus, wombats, more echidnas than you could shake a stick at, and even a beer-drinking pig named Priscilla.14
The bumblebees seemed to have taken very well to Tasmania, having now spread throughout the island from the wild and windswept west coast to the sunny north-east. This despite recent genetic evidence suggesting that they were all the descendants of a very small number of queens that made it here in 1992 – perhaps just one or two – and hence all horribly inbred.
What we didn’t see this time was Tasmanian devils. Whilst the roads were still as littered with corpses as they were in 1999, where previously the devils had comprised perhaps a quarter of the body count, now there were none. The poor brutes have been afflicted by a grotesque plague, a deadly facial cancer which is infectious and spreads when they bite each other – which being rather bad-tempered beasts they are prone to do. No one knows where it came from, but it is most likely a disease accidentally introduced by man. It has all but wiped them out, so perhaps I will never now see one in the wild.
Once back in a frightfully cold Scotland (the temperature in December 2010 regularly fell to -20°C), I set about analysing the data. Overall, we found 76 per cent more plants in 2010 than in 1999, with many coastal populations having doubled or tripled in size. The conclusion is that it does look as if lupins in Tasmania are spreading and likely to become a major problem in the future.
