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Biologists race against time to save South Florida butterfly

Search teams scoured the mosquito-filled tropical forest of this island in Biscayne Bay on Wednesday in what one scientist called a race against time to save one of the world’s rarest butterflies.

Time is winning so far. And running out.

After nearly a month of surveys in the prime breeding grounds of the Schaus swallowtail butterfly, there have been just three confirmed sightings. Worse, only one was a female desperately needed for a captive breeding project that could be the last, best hope for an endangered species found only on a few islands in the bay and on Key Largo.

The situation is so dire that the U.S. Fish and Wildlife Service took the rare step Tuesday of issuing an emergency order authorizing the capture of up to four females for the breeding effort.

“It doesn’t guarantee survival, but it would put us in a better position to save this species,’’ said Jaret Daniels, a University of Florida butterfly expert leading the project.

If, that is, anybody can manage to slip a butterfly net over a few females.

With the brief “flight season’’ of adult Schaus swallowtails typically ending around mid-June, chances of even seeing one grow slimmer each day. Like most hunts this year, Wednesday’s struck out.

Biologists from the federal wildlife service, Florida Fish and Wildlife Conservation Commission, Biscayne National Park and University of Florida, aided by two UF research students, spent hours surveying the tropical hardwood hammock at Elliott’s southern tip. It was not exactly a pleasant walk in the park, requiring head-to-toe mesh “bug suits” to ward off black buzzing clouds of mosquitoes.

Decades ago, hundreds of Schaus swallowtails — hand-sized butterflies with brown-black wings accented by swirls of yellow – would typically be in the area called Petrel Point at this time of year, slowly flitting along trail edges and around the torchwood and wild lime trees that are prime “host plants” where they lay their eggs.

Last year, 35 were spotted on Elliott; six more in Key Largo. This year, they’re even fewer and very far between – five sightings overall since May 11, and only three confirmed.

“But hope springs eternal,’’ said Akers Pence, a University of Florida butterfly expert.

Because butterfly pupae can survive dormant for several years, biologists can mount capture efforts again if they strike out in this waning flight season. But without some boost from captive breeding, the Schaus could be fast slipping toward extinction.

“It’s definitely an alarm flag that the population numbers are so low,’’ said Daniels, who is assistant curator of Lepidoptera for the Florida Museum of Natural History in Gainesville. “It’s premature to say anything beyond that yet.’’

The breeding program, which helped boost the population in the mid-1980s and 1990s, would only temporarily remove females from the wild. They’d be confined for four days in a 12-by-12-foot mesh cage around native host plants. Technicians would collect any eggs laid on the plants, and then release the females back into Elliot’s tropical thicket. The eggs would be taken to a Gainesville lab to create a new captive breeding population that could help restock Elliott and other promising locations.

Like several other South Florida butterflies — most notably the Miami Blue, which is now confined to a few colonies in isolated islands off Key West — the Schaus has been in decline for decades. It was first listed as “threatened” in 1976 then elevated to the most serious “endangered’’ category in 1984 as the population plummeted, largely as a result of pesticide spraying for mosquito control and development destroying coastal forests they call home.

But the most recent drop-off is a bit of a mystery. Schaus breeding is typically tied to South Florida’s weather patterns, with butterfly larvae feeding on the tender new growth of torchwood and wild lime that sprout during rainy season. After two very dry years in 2010 and 2011, scientists had hoped for a boom with all the rain this year. Instead, it’s been an epic bust.

The Schaus also has some peculiarities that make it particularly vulnerable. Unlike most other tropical species, Daniels said, it has a short breeding window, typically producing only one generation rather than multiple generations of offspring a year.

Mark Salvato, a biologist with the Fish and Wildlife Service, called the decline “distressing’’ and reflective of an ailing ecosystem. Butterflies are pollinators and the adults and their larvae are part of the food web of tropical hammocks.

In an effort to expand potential breeding habitat, Biscayne National Park has just planted a large stand of young torchwood trees near the Elliott Key marina. But Elsa Alvear, the park’s chief of resource management, said it’s clear that the Schaus will need more help from humans to ensure it doesn’t vanish.

“It’s fingers crossed that we find a female,’’ she said. “It’s really a race against time.’’