The New Nature Page 16
When fruit and vegetables go to market, frogs often go too. The number of frogs on the move at any one time beggars belief: 8 000–10 000 are said to enter Victoria each year, mainly on bananas. Another 7000 come to Sydney. The national guesstimate is that 50000 frogs are on the move each year. Thirteen species travel on fruit into Victoria and New South Wales. Other fruit travellers include pythons and once even a taipan. Frog carers in Sydney and Melbourne visit markets and stores to save stray frogs, which often become pets. (They aren’t returned to the wild for ecological reasons.) Gerry Marantelli, who runs Victoria’s Lost Frogs Home, tells interesting tales: ‘A person has gone to Coles to buy a bunch of bananas, and they’ve put them in a plastic bag and brought them home and put them in a bowl, and then a frog has hopped out. This happened once with a giant tree-frog from north Queensland 8 centimetres long. Not only had the farmer not noticed the frog, but nor had the packer, nor the supermarket staff, nor the lady who bought the bananas. And she’d paid by the kilogram for the bananas. Actually it’s a cheap frog, because in the pet trade the frogs are $50 or $60 each.’
Bananas carry the most hitchhikers, because frogs wedge themselves into the gaps in the hands. Most hop away at the farm when the bunches are hosed down or washed in soapy baths, but in winter they are often torpid and disinclined to flee. Movement of fruit probably explains how Australian dwarf sedge-frogs (Litoria fallax) come to be living beside the airstrip on Guam, an island well north of New Guinea. The same goes for the green tree-frogs now found on Booby Island, a lighthouse island in Torres Strait, and for other frogs turning up in odd places, including the sedge-frog heard calling in a Melbourne quarry far south of its natural range. But frogs, unlike redbacks, don’t do well from hitchhiking, most of them dying after reaching markets.
A frog arriving in bananas or kept illegally as a pet evidently gave Tasmania a new disease. Dying platypuses with weeping and sometimes maggoty ulcers that are blamed on a fungus, Mucor amphibiorum, have turned up in several Tasmanian rivers. Mucor has an odd history. It was first discovered in Germany in 1972 on a green frog imported from Australia. It was later traced back to Queensland, where it lives on frogs (and cane toads) and grows in soil. Queensland platypuses (and frogs) aren’t fazed by this fungus, which isn’t very infective in warm weather. But platypuses in Tasmania lack immunity and swim in colder water. It’s a sorry situation – platypuses dying from a Queensland frog disease – and it shows how dangerous a phenomenon hitchhiking can be. Australia has also imported a frog-killing fungus (the chytrid fungus Batrachochytrium). It was found around Brisbane in 1978 and reached south-western Australia in 1985 and Adelaide in 1996, possibly by travelling on banana frogs.
Australia’s worst crop pest is the Queensland fruit-fly (Bactrocera tryoni), which also travels in fruit. From its native home in the rainforests it travelled long ago into orchards in New South Wales and Victoria, and in February 1989 reached Perth, probably in smuggled fruit. When surveys showed it had spread over a hundred square kilometres around the city, then five months later over 270 square kilometres, the state government swung into battle. Ninety thousand toxic baits were nailed to trees, four in each backyard and others on footpaths, to lure randy males to their deaths. Insecticides were sprayed in almost every affected garden, 22 500 litres a week. Then came the final strike. Thirty million male flies made sterile by radiation were freed across Perth to confound attempts by fertile flies to mate. All this to destroy an Australian rainforest animal far from home. It worked. The last Queensland fruit-fly in Perth was seen in November 1990 (although they returned from eastern Australia a few years later, requiring a renewed attack). These flies have also invaded Mt Isa, Fiji, Tahiti and New Caledonia, even appearing once on Easter Island off South America, all by travelling in fruit. They are another Australian success story to rival the redback.
Insects also hitch rides on live plants. Pandanus trees (Pandanus tectorius), with their wobbly limbs and droopy leaves, are iconic features of Queensland beaches. Like palms, they prove popular in resort towns, a large specimen fetching $1500. During the 1980s a nursery apparently brought some from north Queensland to the Sunshine Coast. Disaster struck. Pandanus trees died in their thousands along beaches everywhere from Noosa to the Gold Coast. Leaves were yellowing and falling off. Primary Industries officer Dan Smith recalled the epidemic. ‘There were about 3200 large pandanus in Noosa National Park in 1995,’ he told me. ‘Three years later half of these were gone, including a lot of the big beautiful ones that people used to rest under for the shade. It was like a fire going through. It was like a graveyard.’ On dying trees Dan found little brown sap-sucking bugs – pandanus planthopper (Jamella australiae). ‘We estimated that one big tree had a population of a million planthoppers. These trees could be 6 metres high and thirty or forty years old but dead within twelve months.’
The bugs were traced back to north Queensland and a search made for their enemies. At Mareeba Dan’s son Nat found planthoppers on pandanus trees in very low numbers. Something was holding them back. Two tiny wasps – less than a millimetre long – were attacking the hoppers’ eggrafts, their larvae eating the eggs. The wasps were brought south. At the same time hundreds of pandanus trees were injected with insecticide. Dan recalled the public reaction: ‘Some people said, “Horror of horrors. How can you think of using chemicals in a national park?” But when you’ve got trees dying like flies . . .’ The work paid off. One of the wasps (Aphanomerus) has brought the hopper to heel. Pandanus seedlings are now rising beneath the skeletons of the dead. But Dan fears the hoppers will now spread north, to Cooloola, Fraser Island and the Whitsunday Islands. ‘There are hundreds of thousands of pandanus in Cooloola,’ he said. ‘It would be pretty hard to inject trees in there.’ With any luck the wasp will follow the bug on its travels. Pandanus trees grow right along the Queensland coast, and we may wonder why the bugs never travelled south on their own. But the trees grow sparsely in some regions, around Bowen for instance, and maybe the bugs never found them. They prefer hopping to flying. They illustrate again the dangers hidden hitchhikers pose.
Palmdarts, tiny butterflies shaped like fighter jets, are riding on Australia’s love affair with palms. Palms beside swimming pools signify the good life for the frond-chomping caterpillars. Surfers Paradise, with all its nibbled fronds, could be called Palmdart Paradise. According to What Butterfly is That?, orange palmdarts are found as far south as Sydney and yellow palmdarts as far south as Rockhampton. That was true when the book came out in 1932, but nature keeps changing. Orange palmdarts now flit about in Melbourne gardens and yellow palmdarts cruise through Byron Bay. Both have also reached Perth, orange palmdarts appearing in a nursery selling Queensland palms.
More serious pests riding around on plants include the weevils (Gonipterus scutellatus) and sawflies (Phylacteophaga froggatti) that blight blue-gum plantations in Western Australia, and tiny wasps that infest Geraldton wax farms. The wasps have even reached California on fresh flowers and attack Geraldton wax farms there. I could pile on more examples – such as paperwasps (Polistes humilis) stinging children in Perth, cicadas (Cystosoma saundersii) in Sydney and Lord Howe Island, butterflies around Alice Springs, and more.
Other passengers in pots include lizards, snails, seeds, and even, on one occasion, an echidna. A slimy little flatworm called Parakontikia ventrolineata, originally from southern Queensland, has travelled on garden plants to Melbourne, Norfolk Island, New Zealand, Hawaii, England, South Africa and North America, and it now lives in all these places. The weasel skinks (Saproscincus mustelinus) found in Canberra gardens probably invaded with tree-ferns from Sydney. You can’t always assume that the bug, lizard or frog in your garden is local. I once heard a north Queensland ornate frog (Cophixalis ornatus) cheeping from a garden bed near my Brisbane home. A stripy snail (Figuladra aureedensis) in central Queensland has reached gardens much further north. No-one gives much thought to all the hitchhikers riding around on plants, but in this world of rapid chan
ge they are something to wonder about, and sometimes something to worry about.
Wood also carries passengers. Canberra’s residents get firewood from up to 500 kilometres away, and customers sometimes receive a bonus reptile. ‘I know they find things,’ biologist Mark Lintermanns told me. ‘They either knock them on the head or they throw them over the fence.’ A survey of Hobart’s firewood found funnel-web spiders, termites, meat ants, cockroaches, wood-boring beetles, earthworms – fifty-six species in all, mostly native. Some of the wood goes to Sydney, where prices are higher. Wood is a Trojan horse that brings scorpions and spiders into cosy homes. In Western Australia lizards (Cryptoblepharus plagiocephalus) have come south on raw fence-posts, setting up homes near the coast. Lord Howe Island was frog-free before shipments of timber (or maybe pot plants) ferried in eastern grass skinks (Lampropholis delicata) and brown tree-frogs (Litoria ewingii).
Animals also stick fast to vehicles. Snail expert John Stanistic was amazed to find stripy snails (Figuladra) of a species unique to central Queensland living in rainforest near Brisbane – 600 kilometres south. The penny dropped when he saw a sign there saying ‘Beware Unexploded Ordinances’. The snails had evidently come south on army trucks travelling from one training camp to another. Earthworms and plants have also founded new colonies after travelling in mud on cars. Some years ago geographer N.W. Wace searched through the settling tanks of a Canberra car wash for seeds, and among the 18566 seedlings he sprouted were six native species not found near Canberra – beach rush (Isolepis nodosa) included. Further south, in Victoria, the winding road into Wilsons Promontory is lined with groves of coastal plants carried inland as seeds stuck to cars. Coast wattle (Acacia sophorae), western Victoria’s worst woody weed, often spreads like this, experts suggest.
Seeds also travel to ports with stock. When the Flemington saleyards (now Sydney Farm Produce Markets) closed in 1968, botanists found 269 plant species sprouting in the dung-drenched earth. Warring for space among foreign weeds were thirty or more kinds of Outback plants brought east in fleeces, fodder and dung. Here were saltbushes, paper daisies, grasses and burrs growing in a big city hundreds of kilometres from home. Many a plant grows somewhere odd because a seed fell from a stock-train or hay bale; for example, the windmill grass (Chloris truncata) found around Melbourne and Adelaide. Journalist Donald MacDonald remembered in 1887 that when sheep were led into Melbourne they camped ‘on every open pasture and common, and in these places strange vegetable forms were continually springing into existence’.
When seeds reach ports they often keep travelling. A hundred and seventy species of native plants have sprouted abroad near wool mills and ports, with a few going on to become permanent weeds. A century ago, below Scottish wool mills, Bogan flea from Outback floodplains carpeted riverbanks like ‘moss’, and swamp dock (Rumex brownii) was growing miles downstream. With hooked seeds that grasp fleeces, socks and sacks, swamp dock has proved a doughty traveller, invading Alice Springs, Perth, Lord Howe, New Zealand, Hawaii and England. It’s a very successful lawn weed that likes my garden.
I could go on with examples – mussels (Spisula trigonella) from eastern Australia invading the Swan River around Perth; spotted marsh-frogs colonising northern Australia (at Kununurra) in houses trucked up from Adelaide; black spear grass (Heteropogon contortus) invading the red centre; orchids (Pterostylis dilatata) spreading south to Perth – but you’ve heard enough.1 So I’ll end on a story that needs telling only because it’s so serious. In 1974 Ross River virus invaded Tasmania. The victims were laid low by the usual symptoms: mood swings, malaise, lost concentration, night sweats, sore joints and a compulsive need to sleep. Some developed Chronic Fatigue Syndrome and had to quit work. Lives were ruined. This disease from the mainland, found originally in marsupials, apparently entered the Apple Isle in the bloodstream of a person, sheep or cow.
If you take just five examples – Ross River virus, redbacks, fruit-flies, Mucor fungus and pandanus planthoppers – hitchhiking adds up to a serious phenomenon; one that will create many new problems in future. In the ‘new nature’ of the future we’ll see many more animals, plants and diseases turning up somewhere new.
1 Other examples are listed in the Source Notes.
‘Release of wildlife into territory foreign to it involves, not a calculated risk, but a risk too great to calculate. The animal moving game, however, proceeds through the land.’
George Laycock, The Alien Animals (1966)
I am lying in a stream in John Forrest National Park near Perth, but although the water is soothing I can’t quite relax – the vegetation around me is too discordant. I know that those silver wattles (Acacia podalyriifolia) and kurrajongs (Brachychiton populneus) up on the bank don’t belong here, nor the cypress pines (Callitris glaucophylla) on the other side, nor the cedar wattles (Acacia elata) round the bend, nor that kookaburra cackling above. I am surrounded by a gaggle of domestic imports brought deliberately from thousands of kilometres away, from the opposite end of this land.
This kind of experience is on offer in many parts of Australia, especially on islands. Often it is made possible not by animals or plants hitchhiking or exploiting habitat change, but by their deliberate release into the wild, or by their escape from captivity or cultivation. This has led to koalas, platypuses, bandicoots, lyrebirds and emus going where they don’t belong, founding what are, in effect, foreign populations. Australia now has ‘exotic kookaburras’ and ‘feral sugar gliders’, and much else besides. The scale of change has been extraordinary.
In South Australia, where statistics are available, thirty-two animal species (mammals, birds and reptiles) have been deliberately translocated, more than 60 per cent of individuals ending up outside their original range. Plants have been moved around too. Many translocations were made with government support, and with never any thought for undesirable consequences. Invasions by exotic pests attract many complaints, but the Australian equivalent – wildlife shifts within the country – seldom rates attention. It’s a complicated story, and I can’t do it justice here.
Aborigines probably spread some plants about in the past. Yams were allegedly planted on north Queensland islands, and the lilly pilly called ‘sorbi’ (Syzygium branderhorstii) was probably spread about by Torres Strait Islanders growing it for fruit. In the Red Centre the Alyawarre recently spread bush tomatoes (Solanum chippendalei) south by bringing fruit to camp in cars and strewing about the seeds. The first colonists moved things too. Crimson rosellas from New South Wales (escaped pets, presumably) won their freedom on Norfolk Island very early on, missionary James Backhouse finding them common by 1835. These ‘red parrots’, as the convicts called them, were perhaps the first translocated animals in Australia. Sugar gliders, taken from Melbourne to Tasmania in the 1830s, were probably the second. Australia by the 1840s already had flourishing populations of feral parrots and possums, setting the stage for everything that followed.
Australians during the 1860s were gripped by acclimatisation fever, which had its roots in England and France. Gentlemen dreamed of filling ‘empty’ lands and waters with exotic riches. Their imaginations soared. There was talk of herding yaks and llamas on farms, and freeing antelope, nightingales and glow-worms in forests. These over-confident meddlers convinced themselves that God’s work of creation was incomplete; that noble work had been left for them to do, redistributing creatures around the globe.
Australian animals figured in their plans. At Adelaide’s first acclimatisation meeting in 1862, George Francis wondered about birds: ‘New South Wales has 88 birds not found here, while we have 16 peculiar to ourselves; Western Australia 36 not found elsewhere, and Tasmania 32. How interesting and useful to exchange all these!’ Interesting indeed. Victoria’s Acclimatisation Society (founded in 1861) had as its second object ‘the spread of indigenous animals, etc., from parts of the colonies where they are already known, to other localities where they are not known’. They especially had fish in mind. It irked them that
fishermen along the Murray could haul in huge cod while the muddy Yarra yielded nothing better than catfish. Thanks to their efforts, by 1862 the Yarra carried cod. Acclimatisers in Western Australia (where fish are even smaller) also coveted cod, and they imported yellowbelly, river blackfish and eels as well. In 1897 an incredible 800 eels were liberated in rivers in the south-west. Murray cod thrived for a time in a lake near Albany, but none of these fish swim free in the west today. In Queensland in 1896 more than a hundred lungfish (Neoceratodus forsteri) were caught in the Mary River, mainly by Aborigines, then brought south in tanks by train and released in waters around Brisbane, where they swim to this day. The Royal Society of Queensland supervised this work upon hearing that lungfish faced extinction, the colonial government footing the bill. (Instead of going extinct, lungfish benefited from the clearing of riverbanks, which let in more light and promoted the growth of water plants.) Fish stocking has a long and sordid history, which is the topic of chapter 14.
Acclimatisers in the west wanted oysters as well as more fish. Oyster beds were laid down at Albany and Fremantle in the 1890s using stock brought from New South Wales and Shark Bay. Others went into the King River: 8000 Sydney oysters and 4000 shells and spat from Shark Bay and northwards. None survived. In 1900 thirty swans were imported. This sounds implausible, inasmuch as black swans are emblems of Western Australia, but the slaughter of local swans was proving so relentless that extinction of a symbol was feared. Hundreds of kookaburras were also imported. They were expected to prey on tiger snakes, supposedly increasing because of ‘top-dressing of the pastures’. By 1918 politician Walter Kingsmill could exclaim that ‘the laugh of the kookaburra is becoming a familiar sound, and applications are coming to hand for more supplies, showing in what high estimation this typically Australian bird is held’. Kookaburras went to Tasmania as well. Today they are thought to be ousting rare masked owls from tree holes in Tasmania and preying on wrens in Western Australia.