It’s the story of the nutria all over again. It’s happening
in Colorado this time, not Louisiana, but the arc is very similar.
The nutria story involves a couple
of invasive species—one plant, one animal—that met up in the southern United
States. In 1884, the water hyacinth was first brought to the US from Japan and
exhibited at the Cotton States Exposition in New Orleans. It’s a lovely plant,
and fair-goers took home souvenirs and planted them; soon, the water hyacinth
took so well to its new home that it was clogging waterways throughout the
Southeast and interfering with navigation. Huge amounts of money were spent in
trying to get rid of it.
Nutria are large, semi-aquatic
rodents—picture a 12-pound rat—imported to the US from South America in the
early 1900s for their fur. In the 1940s, someone realized that nutria did a
terrific job of controlling water hyacinth and other aquatic weeds, and large
numbers of the rodents were released throughout Louisiana, where they thrived.
By the 1950s, people realized that beyond devouring just the weeds, the nutria
were also wreaking havoc with rice and sugarcane fields, damaging marshes, and
actually weakening earthen levees by stripping and eating most of the vegetation
on them. Since then, the nutria have had a checkered fate, both killed as pests
and occasionally (when their numbers dropped so much that the fur industry
protested) placed on the protected species list.
The more recent version of the
story features the tamarisk, or salt cedar—a tall shrub native to central
Asia—and the Diorhabda
elongata, a
smallish beetle from Kazakhstan, also known as the salt cedar beetle. The
tamarisk was brought to the US in the 1800s and widely used for erosion control
and windbreaks. It was also planted for shade. It spread and crowded out native
plants such as cottonwood and willow and formed dense stands that became
wildfire risks, and efforts to control the plant have been ongoing.
Three years ago, the US Department of Agriculture began releasing the
beetle, which eats the leaves of the tamarisk, along stretches of Colorado
streams in an attempt to control the invasive plant without using herbicides. It
worked very well—too well, according to some. Scientists at the University of
Utah, using satellite-mounted infrared sensors, are documenting defoliated areas
along the Colorado River, far outside the areas where the beetles were initially
released. They say the salt cedar beetle is responsible for killing off the
shade-providing tamarisk in areas where the last few breeding pairs of an
endangered bird, the southwestern willow flycatcher, are nesting, and that if
something isn’t done soon the birds will die out in the region.
The Center for Biological Diversity and a chapter of the Audubon Society
are now suing the federal Animal and Plant Health Inspection Service over the
beetle-introduction program. They claim federal officials did nothing to ensure
the tamarisk would be replaced by native shade-providing plants; there is
actually a danger of similarly water-guzzling non-natives moving in to take its
place.
Biological controls like the beetle have been used successfully in many
cases and have provided an alternative to, or at least a way to cut down on,
herbicide use. The Galerucella beetle has been
used in the US for years to control the wetland invasive
purple loosestrife, for example. It’s often hard to predict the long-term
consequences of introducing a new species, but this is a story we’ve heard often
enough that we should be more aware, by now, of the possible surprise
endings.