An adult Bartram's hairstreak butterfly in Everglades National Park/NPS
Searching For Everglades' Elusive Butterflies
By Kurt Repanshek
EVERGLADES NATIONAL PARK, Florida __ In a subtropical landscape that claims nearly 100 butterfly species, Aerin Land couldn't find a single butterfly as we ambled across a stretch of pine rocklands in Everglades National Park, and that was troubling.
This was prime habitat for the Bartram's scrub-hairstreak and Florida leafwing varieties that normally call southern Florida home, but neither fluttered into view.
"This is the pineland croton, which is the host plant for" the two endangered butterfly species, said Land, a fire ecologist with the park. As we squatted on the craggy limestone floor of this section of the park, surrounded by sawgrass palmetto and slash pines, Land pointed to the small, spindly plant, which is both food source and host for eggs from the two species.
"See this bright orange sap that's oozing when the plant's been damaged," she said. "Actually looking at this, I'm a little suspicious that I'm seeing some catepillar feeding on this particular plant. We see little chunks, bites taken out of the side of it. Some consumption down there. Now, there are some patterns of heirbivory that are really indicative, that would definitely be our caterpillars that have done this, and then there are some other insects out here that will munch, or test on this plant.
"This particular pattern, I'm not entirely sure that that was our caterpillar, but it's certainly possible," said Land.
According to park staff, the location of Everglades makes the landscape attractive to butterflies from both Caribbean landscapes and from farther north in the United States. And there also are a few species found only in Florida. A butterfly common to the park and easy to spot year-round is the white peacock, a tan and white butterfly also found in much of South America. More difficult to spot are the Florida duskywing and eastern pygmy blue, which focus on specific plant communites, the park notes.
Although adult Florida duskywings take nectar from a wide variety of plants, the caterpillar form is a pine rockland specialist that relies exclusively on a single species of flowering shrub — locustberry — in its natural habitat. -- NPS
Florida leafwing egg on underside of rockland croton leaf/NPS
The Bartram's scrub-hairstreak and Florida leafwing take this specialization to a higher level, focusing strictly on the pineland croton, a shrub that can grow to 3 feet in height, though Land was leading me through a stretch of the pine rocklands that had been subjected to a precribed burn just two months earlier. The crotons we encountered were relatively recent starts and only a few were taller than 12 inches.
"The pineland croton, its scientific name is croton linearis, it's the only known host plant for the larval stages of both these butterflies, so they can't survive in the larval stage on any other plant," said Land. "So the Florida leafwing will lay its eggs on the underside individually, of a leaf, while the Bartram's scrub-hairstreak will lay their eggs within clusters of flowers."
As we roamed the area, Land would from time to time inspect a pineland croton for either butterfly eggs or signs that caterpillars had been munching on the leaves. Time and again, she failed to find what she was hoping to spot. However, a month earlier, as ecologists were examining how the area burned by the prescribed fire was faring, "we found one of our endangered species of caterpillar munching on one of these (pineland croton) resprouts" in an area just outside the boundaries of the prescribed fire.
"This is a nice illustration of that, if there is an unburned refugia, wildlife will use it. It's just a nice way to tide them over until the remaining area is recovered to a sufficient level for them," said Land.
A mystery that revolves around these two endangered butterfly species is why, with available habitat, they are not increasing in number.
"The kind of larger answer for the initial, 'Why is this endangered?', is habitat fragmentation," she explained. "The pine rocklands ecosystem is one of the highest, driest ecosystems in South Florida, and so that made it the most enticing area for developments of Miami-Dade County, essentially. So, the large part of Miami-Dade County is built upon historic pine rocklands. There are pine rockland fragments all throughout Miami-Dade County, some privately owned ones, and parks, state and county parks, and you'll find pineland croton in those areas. The Miami Zoo has a nice tract of it, but the Florida leafwing is only found in Everglades National Park. It's not been able to thrive outside, and we're not entirely sure why."
One possible threat is the Peter's rock agama lizard, an import from Africa that savors the occasional butterfly meal.
The frequency of sightings the past few years has continued to drop, said Land, "and we're not entirely sure what's driving the increasing rarity. It's telling, too, when you have your most vulnerable wildlife, they're kind of indicator species, that they're starting to suffer, or wink out. It's telling the larger story of an area as a whole."
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