Once analyzed, the data show a clear trend. "Over the past 19 years, a warming climate has been reshaping Massachusetts butterfly communities," notes Greg Breed, lead author on the study and a postdoctoral fellow at the Harvard Forest in Petersham.
Subtropical and warm-climate species such as the giant swallowtail and zabulon skipper -- many of which were rare or absent in Massachusetts as recently as the late 1980s -- show the sharpest increases. At the same time, more than three-quarters of northerly species (species with a range centered north of Boston) are now declining in Massachusetts, many of them rapidly. Most impacted are the species that overwinter as eggs or small larvae, indicating that these overwintering stages may be much more sensitive to drought or lack of snow cover.
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