The Nature Conservancy - Karner Blue, About

The Nature Conservancy
Indiana Chapter

Southern Lake Michigan Rim

Karner Home Page

Project Origin

Rearing and Releasing Karner blue

Description
The Karner blue is a small butterfly with a wingspan of approximately one inch. Males and females can be distinguished by the coloration on the upper surface of the wings. The male is bright blue with a thin black line and white fringe along the wing margins. The female is dark blue near the body turning dark brownish gray toward the edges of the wings. The female also has a row of orange spots on the upper surface of the hind wing that is absent in the male. Both sexes are silvery gray underneath with a row of orange spots along the outside margins of the wings.

Habitat
Historically Karner blue butterflies were found scattered throughout the region that extends from New England west through the Great Lakes into central Wisconsin and Minnesota. They occupied patches of oak savanna and pine barrens that supported lupine, the only known host plant for their caterpillars. In Indiana they occurred in a narrow band along the shoreline of Lake Michigan.

Savannas and barrens are dynamic ecosystems that support a diverse assemblage of grasses and wildflowers along with scattered trees and shrubs. Wildfires played a critical role in shaping these natural communities. Prior to European settlement, periodic fires swept across the landscape killing or stunting the growth of trees and shrubs, which allowed herbaceous plants to flourish. In the absence of fire, woody species colonized areas and quickly shaded out grasses and wildflowers. Variations in fire frequency and intensity created an ever-changing mosaic of habitat patches in the landscape.

Karner blue is one of several species of plants and animals that adapted to habitat patch dynamics in the oak savannas and pine barrens. In large intact landscapes small populations, known as demes, occupy individual habitat patches. Over time, the demes shift across the landscape in response to changing habitat conditions. As butterflies disperse out in search of mates, occasional interactions between individual demes tie the smaller populations together regionally as a meta-population.

Habitat loss is the main cause of declining Karner blue populations. In addition to direct destruction of habitat, fire suppression has lead to extensive habitat degradation. Fragmentation of natural landscapes has impacted the butterfly by disrupting meta-population dynamics. The U. S. Fish and Wildlife Service estimates that over the past 100 years Karner blue populations have declined by 99%, of which 90% occurred in the past 15 years.

Life cycle
After mating the female Karner blue lays eggs directly on lupine plants. The eggs are about 1 millimeter in diameter. A freshly hatched caterpillars is equally as small. During a period of ten to fourteen days after hatching, while feeding exclusively on lupine leaves, a caterpillar grows to approximately 20 millimeters in length.

The next stage in development is pupation. The process begins with the caterpillar shedding its outer shell and attaching itself to an appropriate substrate. Over the following seven to ten days it will complete the metamorphosis into an adult butterfly. During that time the development of external features such as wings, antennae, legs and eyes is clearly visible.

The process culminates with the emergence of an adult butterfly. The outer protective shell splits near the head and the butterfly uses it legs to crawl out. The wings begin to expand immediately as the butterfly searches for a protective spot. For about forty-five minutes it hangs motionless as its wings dry.

Karner blues are most commonly seen fluttering low to the ground in large sunny open areas searching for mates and feeding on nectar from a variety of wildflowers. After mating, females spend most of their time moving among lupine patches were they lay their eggs. On average, the adult lives for about a week in the wild.

There are two broods of Karner blues per year, one in late spring and another in mid summer. In early May caterpillars begin hatching from eggs that were laid the proceeding summer. Adult butterflies usually emerge at the end of May into the first week of June. Eggs from the first brood begin hatching in mid June. The peak adult second brood flight is mid July. During the second brood females once again lay eggs directly on the lupine. As the plants die back for the year the eggs remain on the dead vegetation where they over-winter. The following spring the process begins again.

back to top

Karner Home Page

Project Origin

Rearing and Releasing Karner blue

Back to Southern Lake Michigan Rim page