Baltimore Checkerspot Butterfly

Photo by Erik Nielsen - 6/30/2002

Turkey Hill Reservation, Hingham

Photo by Fred Goodwin - 6/18/2002

At the Mill Pond in West Newbury

Larva on ash seedling

Photo by Erik Nielsen - 6/30/2002

Turkey Hill Reservation, Hingham

hoto by Frank Model - 7/12/2007

Moran Wildlife Management Area, Windsor

Male

The Baltimore checkerspot butterfly sent the results of annual census of the fluttering creatures fluttering off the chart this summer, according to results released on Wednesday by the Audubon Society of Rhode Island.


More than twice as many butterflies -- 7,221, of many species -- were counted this year in a two-day period than in 2008, said July Lewis, volunteer coordinator for the nonprofit environmental organization, whose headquarters is in Smithfield.

That increase was almost entirely due to the checkerspot, the state butterfly of Maryland, which mysteriously has taken up residence in dense numbers in a privately owned field in Bristol, Lewis said. The volunteers tallied 3,240 checkerspots.

"The population of the field is unusual for sure," she said. "We are looking into it. It's fascinating. I think we found 40 checkerspots in the whole rest of the state. This one place is very unusual."

M. Deane Bowers, a professor from the University of Colorado who is spending a sabbatical at Brown University, said in an Audubon news release, "In over 30 years of studying the Baltimore checkerspot, I have never seen a population this size."

The vivid orange and black checkerspots are native to the East Coast, but are much more common in Southern states.

Lewis said the checkerspots' favorite chow used to be the turtlehead plant, which is not very abundant in Rhode Island. For that reason, she speculated, the population of checkerspots remained low.

But starting some time in the 1980s the checkerspots' caterpillars switched to English plantain.

"The turtlehead is restricted to wetlands, but plantain is found everywhere, even in cities," Lewis said. "They eat it right down to the nub."

Bowers said that the voracious caterpillars ate their way through the field and began crossing a road to find more food.

Lewis said that Audubon had been aware of the Bristol field for some time, but the sheer size of the butterfly numbers had made it "daunting" in the past to contemplate doing a proper census.

"This year we said, 'Darn it, we're going to get a team together,' " she said.

So volunteers lined up abreast and marched through the field like searchers looking for a lost child. And as they went they "took a transect" -- scribbled their findings down as they plowed along.

The North American Butterfly Association organizes a census every year across the continent, Lewis said. "They call it the Fourth of July count, because that's when they start."

The census takers mark out a circle 15 miles in diameter and count everything they see. There are five such circles in Rhode Island, each one in a different county.