HOW WEIRD IS this? The Azores Islands in the North Atlantic had a critically endangered plant, a clover fern (Marsilea azorica) known from a single roadside pond, that experts looked at closely and realised was a fern from Australia, known here as hairy nardoo (Marsilea hirsuta). The species is sold in the aquarium trade and was probably put in the pond. Something deemed unique turned out to be just an import from Australia.
Australia can seem like it is over-run with species from Europe, with rabbits, foxes, sparrows, thistles and the like, but some of the traffic has gone the other way. Large numbers of Australian species live in the wild in other countries, all over the world.
Britain, for instance, has Australian wallabies, crustaceans, spiders, beetles, bugs, moths, plants and fungi, among others. Small numbers of red-necked wallabies bounce about in Scotland, Ireland and England, following releases or escapes from zoos and game parks. Their numbers plunge during harsh winters.
The Australian barnacle Elminius modestus has displaced native barnacles across much of southern England and Wales. (Image: Auguste Le Roux / Wikimedia)
Something else that hops is the woodhopper (Arcitalitrus dorrieni), also called the land shrimp, a tiny Australian crustacean that feeds at night in gardens and woodlands from southern England to Scotland.
The woodhopper may have reached the British Isles on imported Australian treeferns (Dicksonia antarctica). These have spread from gardens into the wild on Valentia Island in Ireland. Other garden escapes from Australia include blackwood (Acacia melanoxylon), a wattle that sprouts on cliffs in Devon, and pigface (Carpobrotus glaucescens), found near beaches on the Channel Islands.
These examples are trivial, but some visitors from Down Under count as serious. The tiny Australian spider beetle (Ptinus tectus) long ago became a major global pest of stored grain. Australian mealybugs (Pseudococcus calceolariae) and groundsel rust (Puccinia lagenophorae) attack cultivated plants in Britain, although the rust is valued when it kills groundsel, a weed. The Australian barnacle (Elminius modestus) has displaced native barnacles across much of southern England and Wales. But it is native to New Zealand as well as Australia, inviting questions about which country it came from. It probably hitchhiked on early wooden ships.
Invaders from Australia are more serious in southern Europe where the winters are mild. On the Azores, part of Portugal, Australian sweet pittosporum (Pittosporum undulatum) and blackwood are two of the worst landscape weeds. The pittosporum is taking over habitat of the endangered Azores bullfinch. Mainland Portugal has serious problems from wattles and hakeas swallowing up dunes and other places. Australian wattles have managed to become serious weeds on every continent bar Antarctica. Sweet pittosporum is a problem in such far flung places as Jamaica, Brazil, New Zealand and South Africa.
Many scientists say that Earth has entered a new epoch in which humans are changing everything. The mixing of species is one feature of what is being called the Anthropocene. It means a world in which we curse the weeds and pests brought into Australia, while people elsewhere curse species brought out of Australia.
Tim Low is the author of the award-winning book Where Song Began. Follow him on Twitter @TimLow5.