Karner Blue Butterfly: Endangered

Wilton Wildlife Preserve & Park is home to the largest population in the Northeast.


male Karner blue butterfly

Male Karner blue butterfly. Photo credit: Carly Voight

The undersides of the wings are grayish in color with black dots encircled in white.  Both the male and female Karner blue butterflies have a row of orange crescents lining the entire edge of the underside of the hind wing.  The male’s upper side is violet blue with a black margin and white-fringed edge.  In contrast, the female’s upper side is a darker brownish blue color with the marginal orange crescents “showing through” to the upper side of the hind wings.  Both sexes are small with a wingspan of about 1”.

Life Cycle

Female Karner blue butterfly

Female Karner blue butterfly. Photo credit: Carly Voight

Each year there are two broods of Karner blue butterflies, the spring brood and the summer brood.  In mid to late April, larvae hatch from eggs that have overwintered on or near the ground.  The larvae eat the leaves of the wild blue lupine, the only food source for the Karner blue caterpillars.  After 3-4 weeks, the larvae form pupae.  This stage lasts 7-12 days.  The first brood of butterflies emerges from the pupae in late May and early June.  The butterflies feed on nectar from a number of wildflowers, typically traveling no more than 600 feet from where they emerged.  The females lay eggs on the wild blue lupine plant and five to ten days later, the eggs hatch and the cycle is repeated, eventually producing the summer brood of butterflies.  The summer brood’s eggs overwinter to hatch the following spring.  The Karner blue butterfly is short-lived, living an average of 4-5 days.  Some live as long as 18 days.

Additional Information

The Karner blue butterfly was first collected in 1861 in Karner, New York, just outside Albany.  In 1941 Vladimir Nabokov, the famed writer, classified it taxonomically.

The Wilton Wildlife Preserve & Park is one of the few places in New York State and the northeast where the Karner blue butterfly still exists.  Once, it inhabited a geographic band that extended from Maine to Minnesota and north into Ontario, Canada.  Native populations have disappeared from Maine, Massachusetts, Pennsylvania, Ohio, Illinois, and Ontario.

The Karner blue butterfly was placed on New York’s endangered species list in 1977 and on the federal endangered species list in 1992.