Invaders in Paradise

from Wildlife Promise

Every family has holiday traditions. Our tradition for the past several years has been to pack up the kayaks and fishing gear and spend the holidays camping in the Florida Keys at Bahia Honda State Park. Known to most for its turquoise waters and white sand beaches (unusual in the Keys), Bahia Honda is famous among biologists for its amazing flora and fauna, including many tropical rarities.  As the gift shop tee shirts rightly proclaim, this gem of an island is truly an “American Paradise.”

Bahia Honda, a subtropical gem in the Florida Keys, harbors numerous rare plants and animals. Photo © Susan Stein.

Sheltered by the smooth peeling red bark of gumbo limbo trees, our beachside campsite was often alive with the fluttering of butterflies, in particular zebra longwings (Heliconius charithonia). A northern representative of the passion-flower butterflies I associate more with Central and South American rainforests, these striking black and yellow butterflies were attracted by flowers of another tropical shrub bordering our campsite, the bay cedar (Suriana maritima).

Where’s the Native Wildlife?

Miami blue butterfly on Bahia Honda in 2003. This species was last seen on the island in January 2010. Photo: J. Glassberg.

One butterfly we did NOT see was the Miami blue. Until recently, Bahia Honda was one of the last bastions for this diminutive and endangered butterfly. Miami blues were last seen on Bahia Honda in January 2010. All that now stands between this species and total extinction is a precarious population located on small islands nearer to Key West.

The Miami blue once extended from the Dry Tortugas in the south up along the Florida coasts to about St. Petersburg and Daytona. Its decline resulted from a variety of factors, most notably loss of habitat. On Bahia Honda, however, one of the most significant factors in its recent demise has been a flourishing population of non-native iguanas. These introduced reptiles, which can grow to a yard long, have developed a taste for the young shoots of the gray nickerbean (Caesalpinia bonduc), the host plant for the Miami blue’s eggs and larvae. These ill-tempered and voracious lizards appear to have literally eaten the Miami blues into oblivion on this island.

Iguana basking in gray nickerbean, the host plant for the endangered Miami blue butterfly. Photo © Susan Stein.

Because of their insular nature, the Florida Keys harbor many endangered species in addition to the Miami blue, and National Wildlife Federation has played a key role in keeping development from wiping out their habitats. Unfortunately, invasive species like these iguanas can undermine the integrity of even “protected” habitats and as with the Miami blue push species towards extinction. Further up the island chain, for instance, Grassy Key is being over-run by Gambian rats, which can grow as large as housecats and weigh up to 9 pounds! This African rodent was originally released on the island by a breeder supplying the pet trade.

And Everglades National Park, one of the nation’s crown jewels, is the epicenter of an invasion of Burmese python, a non-native constrictor snake that research now documents has almost completely wiped out this sensitive ecosystems rabbits, raccoons, deer, and other small mammals. Although the endangered Florida panther may be too large or cautious to be caught and killed directly by these constrictor snakes, by consuming much of the panther’s food source the snake will almost certainly lead to further declines for this endangered large cat.

Stemming the Invasive Tide

Burmese python have nearly wiped out small mammals in portions of Everglades National Park. Photo: by Bob DeGross, National Park Service.

Invasive species like iguanas Gambian rats, and Burmese pythons not only exact a devastating ecological toll, they also pack an economic punch, costing the U.S. economy an estimated $123 billion a year.

Trying to control these pests once they have established themselves is difficult, costly, and often futile. A far better approach, ecologically and economically, is to keep them out in the first place. One obvious place to start is to better regulate the import of species known to pose a risk to U.S. ecosystems. Last year the U.S. Fish and Wildlife Service, under pressure from NWF and its partners, made a good start by banning the import of four species of large constrictor snakes that were deemed to present just such a risk.

Unfortunately, bowing to political pressure from a small but vocal lobby of reptile breeders, an additional five constrictor snakes that Fish and Wildlife considers to present an invasion risk, such as the reticulated python and green anaconda, were excluded from that import ban. National Wildlife Federation views the listing of these additional constrictors as “injurious species” under federal law to be a top priority in 2013.

The current system for assessing and limiting imports of invasive and potentially invasive species—designed before the days of lightening fast transcontinental shipping and dramatic expansion of the exotic pet trade—is too slow and unwieldy and badly in need to reform. Fortunately, with NWF support, bills introduced in the last Congress propose common sense reforms that would create a new screening system for evaluating the risk of invasion that species pose, and give the Fish and Wildlife Service greater flexibility and authority to make science-based decisions to prohibit or restrict trade in certain live animals. With the start of a new Congress, reintroduction and passage of bills such as Representative Slaughter’s (D-N.Y.) Invasive Fish and Wildlife Prevention Act is an imperative to better protect our nation from the onslaught of new harmful and costly invasions.

Packing up our campsite back on Bahia Honda in preparation for the long drive home is always bitter sweet. There’s next year’s visit to look forward to, sustained by memories of the snappers we caught this time, and paddles through the mangroves and over the clear waters. But the demise of the Miami blue butterfly on the island—one small but important strand of the key’s biological web—is emblematic of what we already have lost in this “American Paradise.”

How You Can Help

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