Status. The Karner blue butterfly is on both the state and federal endangered species lists. Estimates are that Karner blue butterfly numbers have declined by 99% over the past 100 years and 90% over the past 10 years. Historically, the Karner blue butterfly’s range extended from Maine to Minnesota. It has disappeared from Maine, Massachusetts, New Hampshire, Pennsylvania, Ohio, Illinois, and Ontario, Canada. In 1998, butterflies were reintroduced to Ohio. Today, Karner blue butterflies can be found in New York, Michigan, Indiana, Wisconsin, and Minnesota. Scientists believe that the Town of Wilton has the most viable population of Karner blue butterflies in the east.

Life Cycle. The Karner blue butterfly has an interesting life cycle. In April of each year, the Karner blue caterpillar emerges from an egg that was laid the previous summer. As a caterpillar, the Karner blue feeds exclusively on the leaves of the wild blue lupine. After approximately four weeks, the caterpillar advances to the chrysalis stage. After two-three weeks, a Karner blue butterfly emerges from the chrysalis. This usually occurs in mid- to late-May. As a butterfly, the Karner blue mates and collects nectar from a variety of native flower species. The female lays eggs on or near wild blue lupine leaves. Two to four weeks after these eggs are laid, the second brood of caterpillars emerges. The caterpillars feed on the wild blue lupine leaves, enter a chrysalis, and emerge as butterflies. The second brood of butterflies appears in early- to mid-July. These butterflies mate and collect nectar from native flower species. The female lays eggs near the stems of the wild blue lupine. These eggs over winter and hatch the following spring.

Challenges. The Karner blue butterfly needs the open spaces that support the wild blue lupine and a variety of other native flower species. Open space is jeopardized by natural succession stemming from the decline of agriculture, the suppression of natural fire, and development. These events lead to the loss of habitat and fragmentation (the loss of connectivity between population sites). With the loss of habitat, the Karner blue butterfly population will decrease. With fragmentation, the Karner blue butterfly cannot disperse to other Karner blue populations nor can it colonize new sites. Connections between sites are essential for a genetically healthy population.

The over wintering eggs benefit from snow cover. The snow insulates the eggs from harsh winter conditions. If the eggs are exposed to cold temperatures, harsh winds, rain, and sleet, fewer caterpillars will emerge in the spring.

Efforts to Overcome the Challenges. For information about what is being done at the preserve to protect and restore the Karner blue butterfly, click on Overview of Wilton Wildlife Preserve & Park.