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But then, after a 2008 drought followed by cold snaps in 2009 and 2010, the population in Bahia Honda began a significant decline. Green iguanas soon emerged as a likely suspect in their demise.

The large, vegetarian lizards, probably the descendants of pets released by their owners when they grew too big or burdensome, had developed a taste for the nickerbean leaves where Miami blues laid their eggs. The nickerbean was among the only plants to quickly recover from the cold snaps, and the iguanas chewed through them, likely eating any butterfly eggs clinging to the leaves.

Duquesnel got the news that the Miami blue had received an emergency endangered listing while making his way to the old Bahia Honda Rail Bridge, brandishing a noose at the end of a long pole, which he uses to catch iguanas. He had set metal traps baited with sliced cherries, nectarines and strawberries in more restricted areas of the park, and now he was stalking the lizard from the public trail.

That day, there was no shortage of butterflies flitting about Bahia Honda: cassius blues and one ceranus blue, rust-and-gray Eastern pygmy blues, gulf fritillaries, skippers, bright orange sulphurs, a black-winged swallowtail and a handful of other species that fluttered away before they could be identified. Duquesnel also caught four iguanas, but saw no Miami blues.

In the winter, volunteer snowbirds help Duquesnel tally butterflies in the park. They carry clipboards with a picture of the Miami blue alongside pictures of the cassius blue, ceranus blue and nickerbean blue.

“I tell the volunteers you only need to identify one butterfly: the Miami blue. If you can do that, then you can help. Anything else is a bonus,” Duquesnel says.

By helping to record what species are present in the park, the volunteers are supplying Duquesnel and other scientists with data that may help determine if something besides iguanas contributed to the Miami blue’s disappearance. It could be the pressure from development eating up habitat, pesticides, droughts, the effects of climate change, over-collecting by butterfly enthusiasts, cold snaps or accidental harm caused by human behavior _ or something else scientists haven’t identified yet.

But iguanas are something Duquesnel can catch.

When Duquesnel was hired in November 2010, he saw 40 or 50 adult iguanas a day in the park. Now he sees just a couple big ones a day, and they’re harder to catch because they’ve adapted to his hunting and trapping. To keep the lizards guessing, he tries to tag along with tourists walking along the trails.

“They know the difference between looked or gawked at and being stalked,” he says.

It’s too soon to say whether more than a year of trapping iguanas has had any significant impact other than reducing their numbers, Duquesnel said recently. The iguanas he catches now still have bellies full of nickerbean, and the plants show signs of being nibbled, but whether iguanas or insects are to blame, he can’t say.

And if the Miami blue never returns to Bahia Honda, Duquesnel still wants to make the park’s environment better for all butterflies landing there.

“Even if Miami blue goes extinct, we should still remove iguanas,” he says.