NEW WORLDS - The New Wild: Why Invasive Species will be Natures Salvation - page 20

week. 25 The spectacularly fecund colonist has spread to more than fifty countries, from the backwaters
of Bengal to the rivers of China, from Fiji to Australia, from the Louisiana bayous to the Mekong Delta.
It follows humans, feeding hungrily on nutrient pollution from sewage and farm runoff. It turns up in
lakes and wetlands, estuaries and ponds, slow-flowing rivers and irrigation canals. It even has beach-
heads in Corsica and Spain—not helped, as one exasperated researcher told me in 2013, by the fact that
it is on sale to gardeners at supermarkets across Spain. The IUCN lists water hyacinth among the world's
ten worst weeds. The charge sheet includes blocking waterways, destroying fisheries, and harboring dis-
eases. 26
In some places, we know just when it broke loose and transferred from pretty pond adornment to
waterways menace. In the early years of the twentieth century, workers at the Bogor botanic garden in
Java began dumping the unwanted weed over fences into the Ciliwung River. 27 Water hyacinth is now
everywhere in Indonesia. It was first sighted in the wild in South Africa in 1910, reached Zimbabwe
in 1937, arrived in Zambia and Malawi in the 1960s and Kenya by the 1980s, and entered West Africa
via Cameroon at the turn of the millennium. Almost no large water body in Africa remains untouched,
although the extent of infestation varies greatly.
In East Africa the weed entered Lake Victoria, the world's largest tropical lake, after floating down
the River Kagera in Rwanda. One story says that it escaped from ponds in gardens once tended by Bel-
gian settlers there. During the 1990s, the Kagera carried a constant stream of hyacinth clumps into the
lake. In 1994 the weed was accompanied by—and perhaps nourished by—the rotting bodies of tens of
thousands of victims of Rwanda's genocide. From the lake's western shores, the weed spread across
open waters and around shallow, muddy shorelines. By 1998, when I visited, it had covered four-fifths
of the Ugandan shore, and ships took five hours to push through the weed to dock at the Kenyan lake
port of Kisumu.
Fishers at Kusa Bay, south of Kisumu, showed me mats of weed up to six feet thick that had filled
their bay and destroyed their livelihoods. More than fifty fishing boats were marooned on the weed-in-
fested shore, the fish warehouses were permanently locked, and the old shorefront hotel was derelict.
There was hyacinth as far out into the lake as the eye could see. It harbored snakes, crocodiles, hippos,
snails that carried schistosomiasis, mosquitoes that transmitted malaria, and clods of feces that might
have contained cholera. One small village on the lakeshore had lost five people to crocodiles and three
to hippos in the previous year.
In Uganda, at the hydroelectric plant on Owen Falls, four boats fittedwith rakes and conveyor belts
struggled to keep the weed clear of the turbines. At Port Bell outside the capital, Kampala, a floating
harvester, built just for this purpose in Britain, sank under the weight of weed on its first day in the lake.
In any case, the IUCN's Geoffrey Howard told me, harvesters “just create space for the plants to grow
into.” Herbicides had failed. In despair, scientists had deployed two species of South American weevil
( Neochetina eichhorniae and N. bruchi ) that ate the weed's leaves. If they eat enough, the leaves dry out
and weevil larvae can tunnel into the stem, eventually killing the weed. Weevils were credited with lim-
iting the spread of smaller infestations in India, Thailand, Florida, Java, and Zambia. But when I visited
the fisheries research station near Kisumu, where large numbers of weevils had been bred and put into
the lake over the previous two years, water hyacinth still grew with alacrity. “The bugs can only eat so
much,” one researcher told me.
It seemed hopeless. And then everything changed. Less than a year later, the weed was in rapid re-
treat, Kisumu's port was open, cargo boats moved with ease, and fishers were back in business. What
happened? Some claim it was a success for the weevils. 28 They must have helped, but what had changed