by Dave Goulson
This then begs the question: how can bees tell how old a scent mark is? If it doesn’t evaporate, then it will not fade over time, and it should be impossible to know whether the flower has had time to refill with nectar, yet clearly the bees somehow do know. We still don’t have a definitive answer. My guess is that perhaps the chemicals deposited by bees’ feet slowly sink into the waxy coating of the flower – for just as bees are waterproofed with oils, so flowers are waterproofed with oils and waxes – and by sinking into the flower’s surface they become less detectable, and effectively fade even though they are still present.
Interestingly, the same smelly footprints, when encountered in a different context, have a different meaning. Bee footprints around the entrance to the nest, rather than having a repellent effect, help returning foragers to find their way inside. It seems that bumblebees learn to interpret a particular smell in an appropriate way, depending on the circumstances in which they encounter it.
It is humbling to reflect that though a bumblebee has a brain smaller than a grain of rice, it has powers of perception and learning that often put us mammals to shame. Next time you are sitting in your garden while the bees are visiting your bee-friendly plants (if you haven’t got any, I hope you’ll plant some next spring), take the time to watch what they are doing. You will quickly notice them dismissing some flowers after a quick sniff. But I’m sure that there is still much more to learn. Certain flowers seem to be visited by particular species of bee, and often we have no idea why. Individual bees may collect pollen or nectar or both, and seem particularly disposed to collect one or other depending on the flower, but again we often have no explanation for their choices. On some days, even in high summer when the weather is fine, foraging bees may suddenly become scarce, as if they have all decided to go on strike for a few hours; we do not know why. Bumblebees are one of the most familiar and intensively studied of all the insects on earth, but there is still an enormous amount that we do not understand about their lives.
CHAPTER SEVEN
Tasmanian Devils
Burly, dozing humblebee,
Where thou art is clime for me.
Let them sail for Porto Rique,
Far-off heats through seas to seek.
I will follow thee alone,
Thou animated torrid-zone!
Ralph Waldo Emerson (American poet)
In Tasmania the first bumblebee was recorded in 1992. There was no mistaking her, for the local bee species are tiny – small enough to hide under a grain of rice, mostly drab and not very furry. Nor do bumblebees naturally occur anywhere near Tasmania, for they are mainly creatures of the northern hemisphere. So these new furry giants would not have escaped notice for long, especially since they first appeared in the gardens of Hobart, the most densely populated area of the island.
These new arrivals were quickly identified as buff-tails. Now buff-tailed bumblebees only actually have buff tails in the UK. In the rest of Europe, buff-tailed bumblebees have white tails, which, as you might imagine, makes them awfully hard to distinguish from white-tailed bumblebees. Anyway, these were buff-tailed buff-tails, which meant that they had to have originated from the UK, 10,500 or so miles from Tasmania. If your geography is a little rusty, Tasmania is the southernmost state of Australia, a roughly triangular island floating 150 miles off the south coast of the mainland, with New Zealand lying about 1,500 miles to the east. So how did they get there? The answer is not quite as mysterious as all that, for as I have already mentioned, English buff-tailed bumblebees have been living quite happily in the wild in New Zealand since 1885 or thereabouts. The Tasmanian bumblebees presumably came from there, but this is still a 1,500-mile journey against the prevailing wind, across a stormy and cold Tasman Sea. With the best will in the world they could not have flown.
We may never know how they made the journey. They may have been accidentally transported on a ship; a young queen may have hibernated in a plant pot and been brought over with some nursery plants. But I find this unlikely. It is probably no coincidence that in about 1988 tomato growers the world over turned to using bumblebees to pollinate their crops. Researchers in Belgium and Holland had discovered that bumblebees are fantastically efficient at pollinating greenhouse tomatoes, and they had also worked out how to breed buff-tailed bumblebees in large numbers. As a result, bumblebee-rearing factories quickly sprang up in Europe and then in North America and Asia to cater for the demand. The only tomato growers left out of the bumblebee bonanza were those in Australia, where there are no native bumblebees, and where importing foreign species is strictly forbidden. Tomato growers on mainland Australia still have to hand-pollinate their plants; teams of workers are employed, each of whom is equipped with a slender vibrating wand. Every flower has to be touched with the tip of the wand if it is to set fruit. As might be imagined, this is tedious work in a large glasshouse – some commercial operations cover hundreds of acres and contain literally millions of tomato flowers – and the labour costs are substantial. Bumblebees are not only much, much cheaper, but the tomatoes produced by bumblebee pollination are also larger and apparently taste better than those pollinated by humans, so in the late 1980s, Australian tomato growers suddenly found themselves at a distinct disadvantage. That bumblebees mysteriously arrived in Hobart in 1992 may just be coincidence. Bumblebees had failed to cross from New Zealand to Tasmania for 100 or so years, but suddenly they managed to do so just after it was discovered that they had huge commercial value. Draw your own conclusions.
Yet why shouldn’t bumblebees be imported to Tasmania and, for that matter, to mainland Australia? After all, they are cute, furry and beneficial insects which pollinate crops and wild flowers. Who wouldn’t want them? The answer is that man has a rather poor record with regard to introducing non-native species, and nowhere more so than in the Antipodes.
Australia is a remote island, with a remarkable and unique fauna, of which the bizarre marsupial mammals are the best known. Only distantly related to the mammals found in most of the rest of the world, they evolved into many wonderful forms: kangaroos, bandicoots, koalas and numbats, among numerous others (and top marks to the Aboriginal people for giving them such memorable names). Australia also has thousands of indigenous bees, butterflies, flowers and so on. New Zealand is the same, only more so as it is even more isolated than Australia, so no mammals got there apart from bats (which, of course, can fly). There, giant flightless birds took the roles of large mammals, and enormous crickets (known as weta) evolved to fill the role of mice. When Captain Cook first arrived, New Zealand was clothed in verdant forests teeming with birds and insects, almost every one of which he had never seen before; they were all unique to New Zealand.
Tragically, the early European settlers in Australia and New Zealand soon became homesick, pining for such familiar creatures as foxes, rabbits and hedgehogs. They formed Acclimatisation Societies, dedicated to introducing as many non-native plants and animals as possible, and awarding medals to those who were most successful or dedicated in their efforts. With spectacular naivety, in New Zealand they even experimented with introducing zebra and giraffe. Aside from these, the introductions were remarkably successful. When I first flew to Christchurch (with Mick Hanley in 2003) it all looked tremendously familiar. We had left behind a cold and drizzly winter’s day in London and arrived to glorious summer sunshine, but there the dissimilarity ended. Perhaps not surprisingly, the buildings in Christchurch look decidedly British. After all, all the older ones were built by British immigrants. The trees lining the streets are limes and planes, just like those in London. The birds chirping from their branches were blackbirds, sparrows, thrushes, starlings and greenfinches. We hired a car and drove out of the city across the Canterbury Plain, the main agricultural region of New Zealand. So far as I could tell as we rocketed along with Mick at the wheel, the blurred trees, roadside flowers and farm animals that we shot past appeared to be much the same as those at home. When we stopped – in my case, saying a silent p
rayer of thanks that I had survived the journey so far – a pair of goldfinches flew by, and skylarks trilled overhead. Had it not been for the snowy mountain peaks in the distance, we could have been in Cambridgeshire or any other flat, agricultural part of lowland England.
It was several hours and 300 miles before we saw something new; a small friendly bird which my bird guidebook suggested was a fantail. New Zealand is famous for its beautiful scenery (think Lord of the Rings), but it is an ecological holocaust. In 200 or so years we have wiped almost all the native animals from vast tracts of the country, clearing native forests to make way for farming, and especially for sheep ranching. In the remote mountains there are still forests of native trees, but the birds that once inhabited them have mostly gone, eaten by the introduced foxes and stoats, against which the native species seem to have no defence. Famously the kakapo, a chubby moss-coloured flightless parrot, attempts to escape from predators by shinning slowly up the nearest shrub and then jumping from the top, only to thud down to the ground a yard or so from where it started. Hardly enough to throw a wily fox off its trail. Hence this once widespread New Zealand bird was down to about sixty individuals at the last count.
The situation is almost as bad in Australia, where the native marsupials have struggled to cope with introduced pigs, rabbits, foxes, cats, camels, dogs and goats. Vast tracts of forest have also been cleared to make pasture for cattle and sheep, and have subsequently become overrun with European weeds such as the appropriately named Patterson’s curse,11 while the tropical north-east is swamped with the South American shrub Lantana. Perhaps most famously, cane toads (also from South America) have bred in their countless millions in Queensland, from where they are spreading remorselessly southwards, consuming everything that they can fit into their capacious mouths.
You get the picture: introducing non-native species can have disastrous consequences. But surely bumblebees are beneficial insects? What harm could they do? Well, probably quite a lot actually, although we don’t know for sure. That was why I went to Tasmania in January 1999, with my PhD student Jane Stout. The introduction of bumblebees there was a huge experiment (albeit a very poorly designed one, with only one replicate – Tasmania – and no control). Here was an opportunity to see at first hand what an introduced species might do (and, of course, to escape from the British winter for a few weeks).
We first needed to find out exactly how far the bees had spread. At that time they had been on the island for about seven years, and as the anecdotal records suggested that they had been spreading steadily north and south from Hobart, we hired a tinny little car and set about driving the length and breadth of the island.
Tasmania is stunningly beautiful. The population of less than half a million mostly live in or near Hobart in the south-east, leaving much of the remaining 26,000 square miles very sparsely populated. To the west, the island becomes mountainous and largely inaccessible, clothed in temperate rainforests containing dense stands of giant tree ferns, above which tower the tallest flowering plants in the world, the mountain ash, which grow to well over 300 feet. True to their name, these forests rely on the near-incessant rain coming in on the prevailing westerly winds; they have a damp, gloriously musty scent and prehistoric feel. By contrast, the north and east of the island comprise lower-lying, rolling countryside, with much of the natural forests cleared to make way for farming, mainly sheep ranching. The coasts have some of the most spectacularly scenic sandy beaches I have ever seen, although even in summer the water is a tad chilly. The coastline is somehow made more atmospheric by the knowledge that there is nothing but icy ocean between Tasmania and the South Pole.
One of the joys of visiting Australia for the first time is seeing flocks of wild parrots. Even in the centre of Hobart, flocks of swift parrots live up to their name by rocketing like emerald-green darts from gum tree to gum tree, acrobatically drinking nectar from the flowers and squawking raucously. Beautiful red, yellow and blue eastern rosellas also stride cheekily among the picnickers in the parks, scavenging scraps of food. I had never seen a parrot outside a cage before, and it was wonderful to see these brilliantly coloured creatures living free. I was also particularly keen to see some of the island’s mammals as we toured. I had read that Tasmanian devils were not uncommon, and I was desperate to see one (perhaps just because I was very fond of the cartoon series, although I didn’t really expect them to spin on the spot like miniature tornadoes). Unfortunately these mammals are largely nocturnal, which makes live ones hard to spot, but in an echo of my childhood, dead ones littered the roads. Just as the fauna of Australia and New Zealand has coped poorly with introduced predators, so it seems that the Tasmanian marsupials are spectacularly inept at avoiding cars, for we saw hundreds of corpses. After a few days I gave up hope of ever seeing one alive, and took to photographing the roadkill, building up a fine collection of photographs, including squashed Tasmanian devils, pademelons, bettongs, possums, wombats and potoroos (such wonderful names).
Eventually we did come across one live mammal, in the form of the amazing echidna. From a distance echidna resemble rather chubby, rounded hedgehogs, but close up there are a number of obvious differences. The snout is much longer, tapering to a blunt tip. The spines are enormously thick, more like the quills of a porcupine. And the spade-like feet possess massive claws, enabling the echidna to rip apart termite nests or to dig vertically downwards in times of trouble. In fact once we had seen one, we suddenly starting spotting them on most days. Echidnas are monotremes, members of an obscure group of mammals which includes only themselves and the platypus, both famous for being egg-layers. We eventually met five echidnas in the course of our travels, each of which delayed us for quite some time as we felt compelled to watch them lumbering and snorting about their business like miniature spiny bulldozers. Now when I am asked to name my favourite mammal, I always answer echidna.
Of course we were supposed to be looking for bumblebees, and perhaps part of the reason that we were so easily distracted is because it was proving difficult to establish the distribution of a smallish creature such as a bumblebee in a few weeks over a huge area. Whenever we found one, it was easy enough to mark its location on the map. But when we didn’t, it was hard to say whether that was because there weren’t any, or because we’d been unlucky, or because there weren’t many bee-friendly flowers in that particular place. However, it quickly became apparent that one of the best ways to find bumblebees was to find a well-tended garden with lots of flowers in Hobart itself. Tasmanians are enthusiastic gardeners, perhaps because the climate is particularly benign, but for whatever reason Tasmanian gardens are often rather splendid. Lavender in particular grows well and bees love it. In any garden in Hobart, so long as there were a few lavender bushes, we found that we were guaranteed to see a bumblebee within a few minutes.
So our strategy became one of finding the most colourful garden in each town or village as we drove around Tasmania. We would then either peer in over the fence or, if that wasn’t possible, knock on the door and ask if we could look for bumblebees in their garden. I guess that crime rates there are low. I’ve tried the same approach in Britain and generally received short shrift from homeowners who clearly thought this a flimsy and highly implausible excuse for casing the joint. A strange man on the doorstep holding what is often mistaken for a very odd-looking fishing net in one hand and a cluster of urine sample tubes in the other rarely gets a good reception. In contrast, we were universally welcomed by Tasmanians – perhaps helped by the fact that I usually got Jane, who has a very friendly smile, to knock on the door, and also because experience has taught me to hide the tubes. The only downside to the Tasmanians’ welcoming attitude was that we often then became embroiled in very long conversations obliging us to explain what bumblebees were and what we were doing, listen to long accounts about other interesting creatures that they had seen in their gardens, have a cup of tea and so on – all very agreeable but not terribly productive.
The more r
ural areas, particularly in the west of Tasmania, were harder because there we encountered huge areas with no people, and hence no gardens. We would search for bees on patches of flowers growing by the roadside, one of the more striking of which were tree lupins. These are the North American relatives of the lupins we commonly grow in our gardens, but they are much larger as one might guess from the name, although ‘tree’ is pushing it a bit – they are rarely more than 6 feet tall. They were apparently introduced to Tasmania in the 1920s in an attempt to stabilise the coastal dunes; in their native California, tree lupins thrive on very sandy soils. (Of course this begs the question why dunes need to be stabilised. They’d presumably been perfectly happy for thousands of years being unstable.) Anyway, the flowers are bright yellow, and stands of tree lupins make a splendid sight. As bumblebees love them, we took to searching for them in the areas where there were no gardens, and spent a very pleasant couple of weeks touring Tasmania and producing a distribution map. It was clear that the bees had spread a long way; roughly 60 miles north and south (reaching the southernmost tip of the island), and about 50 miles west. So far as we could tell, they had not reached the north of the island, and we could find none in the dense forests to the west. The bees seemed to be largely confined to places where there were either gardens or lots of European or North American weeds.
