July 23, 2004

Counting Butterflies

Filed under: Adaptation, Animals

Butterflies are often mentioned as being particularly sensitive to climate change. Yet a recent one-day record for butterfly diversity in northwestern Connecticut suggests current climate is more hospitable than ever.

A new survey just completed in northwestern Connecticut set a one-day record for the greatest diversity of butterflies ever observed in that part of New England.

It is funny how you rarely hear things are going well for plants or animals in today’s world. And you never hear that they are prospering because of global warming (unless you are an avid reader of these pages). Instead, with what seems like alarming frequency, you are presented with stories about how fast things are heading to Heck in a handbag as a result of climate change from anthropogenic activities. Consider a recent article in the July 13, 2004 KidsPost section of the Washington Post:

Global warming also could drive many species to extinction, recent studies have concluded. The Edith’s checkerspot butterfly is an example. It moved its range from Mexico about 60 miles north in the direction of busy San Diego and Los Angeles, where temperatures are cooler but the habitat is not as good for butterflies. The checkerspot is now endangered.

The fact is, it would have been hard for Post writer Fern Shen to have come up with a less accurate description of the actual situation.

The original scientific research on which this (mis)information was based was published in Nature magazine back in 1996 by University of Texas researcher Camille Parmesan. Parmesan went and visited many locations in western North America where there had been historical observations of Edith’s checkerspot, checking to see if the butterflies were still present.

Parmesan found that in the southern end of the range, northern Mexico, the species was struggling, and in the northern end of the range, southern Canada, the species was flourishing. Her primary conclusion was that a warming climate had caused the species range to shift northward. She concluded neither that a) the species had become endangered, nor b) that the species’ overall range had declined.

What she actually found was a northward shift in the butterfly’s range—while the butterfly had lost ground at the southern end of its range, it had gained ground at the northern end. There was no suggestion that there was any net change in the size of the butterfly’s total range.

Furthermore, as you might imagine is the case for a non-migratory species that thrives in the vast array of climates—from Baja California to Southern British Columbia—Edith’s checkerspot is not endangered. It is true that two of the 22 North American subspecies of Edith’s checkerspot are on the endangered list, having gotten there primarily as a result of habitat loss by development—not global warming.

Which brings us to the results of the annual butterfly count from northwestern Connecticut. Each year, University of Connecticut biology professor and entomologist David Wagner, leads a survey of the butterfly population in a small portion in the northwestern corner of Connecticut. Warner’s effort is part of a nationwide survey organized by the North American Butterfly Association (www.naba.org). In the field on July 10 of this year, Warner and about 20 other butterfly enthusiasts found 59 different species of butterflies—the most that they had ever recorded. Although he had yet to confirm it, Warner told the Litchfield County Times (www.countytimes.com) as saying, “I’m thinking we probably set the all-time record for any count in New England.”

Warner went on to say that there is no evidence that overall butterfly population or species richness are on the decline in Connecticut. He did suggest that the numbers from several individual species were dwindling, however. Why? Well at least for two species, the northern metalmark and the columbine skipper, Warner had this to say: “Both species are threatened because of Connecticut’s re-forestation.” As forests grow back, they reclaim open fields and meadows where the wildflowers grow on which these species subsist.

Most other butterfly species were faring much better. Indeed, a particularly rare-in-Connecticut species, the Milbert’s tortoiseshell, was spotted this year because “Milbert’s is absolutely exploding in Canada, and the individuals are pushing down in to Connecticut,” Warner said.

News of a thriving butterfly population and expanding forests apparently has not spread very far outside of entomological circles, however.

Instead, we hear news such as the recent suit filed by Connecticut’s Attorney General Richard Blumenthal is one of seven states attorneys general against the nation’s top five electric power producers in an effort to get them to emit less carbon dioxide. Blumenthal justifies the lawsuit by claiming that CO2 increases will lead to “catastrophic” effects, including “loss of forests and other precious resources.”

Perhaps Blumenthal ought to meet Warner and review the direction that things are really trending in his home state. Then again, sometimes ignorance is bliss.


Parmesan, C., 1996. Climate and species’ range. Nature, 382, 765-766.

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