A Sting in the Tale (12 page)

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 rural 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.

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.