Karner blues rely on wild lupine (Lupinus perennis) as their only known host plant.
Wild purple lupine flowers.
Nectar Plants
Adults nectar on a variety of wildflowers, such as goldenrod and butterflyweed.
A Karner blue butterfly drinks nectar from orange butterflyweed flowers.
Ant tending
Karner blues are tended by ants when they are caterpillars. They give ants sugary dew from their glands, and the ants protect them from parasitism and predation.
Ants tending a Karner blue butterfly caterpillar on the leaves of a lupine plant.
Habitat
Karner blue habitat must have adequate lupine, which can be found in sandy pine barrens, oak savannas, and in the eastern part of its range, lakeshore dunes. These are disturbance-dependent habitats that require ongoing management.
A Karner blue butterfly perches on a yellow flower in a grassy meadow.
A meadow of purple lupine against a clear blue sky.
A pine barrens area with flowering wild lupine.
Karner blues and habitat
Population Dynamics
Karner blue has a metapopulation structure with a few isolated metapopulations.
Largely sedentary, this butterfly rarely ventures far from its natal habitat, or nearby lupine patches.
In 2013, populations experienced a precipitous crash, with extirpation in some states surrounding Wisconsin. Severe weather is thought to have contributed to the declines.
Life Cycle
Adults
This species produces two broods per year (bivoltine), with the first adults emerging in May-June and the second in July-August.
A pair of Karner blue butterflies mating on a tan leaf.
Eggs
First brood eggs are laid singly on lupine stems, then hatch in one week or so. The second brood will lay eggs singly near the base of lupine, and these eggs do not hatch until spring.
A very small ivory Karner blue egg laid on the stem of a wild lupine.
Caterpillars
Caterpillars are present for a few weeks in each brood, and are generally tended by ants.
Closeup of a green Karner blue caterpillar.
Chrysalis
These butterflies form their chrysalises in a variety of locations sometimes on hostplants and nearby vegetation.
Conservation
Listing Status
Karner blue was listed as endangered under the Endangered Species Act in 1992 after declines in population trends were observed, likely due to fire suppression and habitat loss.
Karner blue is still listed as critically imperiled throughout its range. In our study state of Wisconsin, it is listed as vulnerable, while it is critically imperiled in New York.
Recovery Efforts
Habitat Conservation Plan in Wisconsin
The Habitat Conservation Plan was approved in 1999 as a partnership between companies, land managers, and townships in Wisconsin. The plan involves guidelines for managing Karner blue habitat, conducting surveys, and conducting commercial activities without harming the species.
There are now many protected areas where Karner blue populations are managed by these various partners. In the population crash of 2013, Wisconsin saw lower declines than surrounding states - likely owing to extensive recent restoration and land management.
Habitat Maintenance
The Nature Conservancy, in cooperation with the Michigan Prescribed Fire Council and the DNR Landowner Incentive Program, performs this prescribed burn. Prescribed fire in the growing season reduces invasive and stimulates native plants for the Karner blue habitat improvement.
Population Trends
We analyzed data from 21 sites in two states. There was no association in the changes in phenology and abundance, and there was no differences in the trends by states. Our Wisconsin data spans ~1997-2018, and New York spans ~1993-2007. We saw more increases in activity at sites in Wisconsin, which covers the recent management, but about an equal number with declines and no change in activity index. A large majority of sites had large advances in median activity date, but some had no change and one had a large delay.
Examples of the activity trends through time for Karner blue.
Examples of the activity trends through time for Karner blue.
