Background
The frosted elfin is a non-migratory butterfly found in dry, sandy, relatively open habitats arising from natural or human induced disturbance^1,2.  This habitat is essential for growth of the butterfly's larval host plant species, which are primarily wild indigo or wild lupine³.  In Massachusetts, the majority of this habitat is found in sandplain communities on the coastal plain.  Frosted elfin overwinter as pupa, and in Massachusetts emergence of adults occurs from late April to early June⁴.  The flight period (adult phase of life cycle) lasts through mid-June, peaking in mid-May.  Females lay eggs on host plants and larvae pupate by late July.

The range of frosted elfin originally extended from southeastern Canada and the northeastern US, south to Florida, and west to Texas¹.  The species has declined over the past 50 years and is now probably extirpated from Canada and Maine, and is rare throughout much of its range.  Massachusetts is considered to be a stronghold for the species, althought it is listed as a species of special concern in the state³.  Declines are associated with loss of habitat through urban development and forest expansion following fire suppression⁵.

Climate Impacts
Several studies have noted that the observed date of first flight for frosted elfin is strongly related to temperature^6,7.  Warmer temperatures during the spring advance the timing of adult emergence, implying that a warmer climate will alter the timing of life cycle events.  Over the period from 1986-2009, sighting dates of frosted elfins advanced 7.6 days in Massachusetts.

In addition, from 1992 to 2010, butterfly species with a northern distribution have generally been declining in abundance in Massachusetts while those with a southern distribution have generally been increasing in abundance⁷.  These observed trends were not found to be correlated with habitat or landscape change and strongly support the conclusion that these trends are being driven by changes in climate.  Frosted elfin are considered to be at the northern extent of their range in Massachusetts, and were found to have one of the fastest growing populations over this period.  This growth may be partially due to management actions aimed at protecting this rare species; however, researchers suggest that it may be partially due to a more favorable climate in Massachusetts.  Based on these observations, it seems likely that a warmer climate in Massachusetts will be favorable for populations of frosted elfin.