The Karner blue (Plebejus samuelis) is an endangered species of small blue butterfly found in some Great Lakes states, small areas of New Jersey, the Capital District region of New York, and southern New Hampshire (where it is the official state butterfly) in the United States. The butterfly, whose life cycle depends on the wild blue lupine flower (Lupinus perennis), was classified as an endangered species in the United States in 1992.
First considered a subspecies of Plebejus melissa, it was first identified and described by novelist Vladimir Nabokov. The name originates from Karner, New York (located half-way between Albany and Schenectady) in the Albany Pine Bush, where it was first discovered.
In the novel Pnin, Nabokov describes a score of Karner blues without naming them.
Local conservation efforts, concentrating on replanting large areas of blue lupine which have been lost to development (and to fire suppression, which destroys the open, sandy habitat required by blue lupine), are having modest success at encouraging the butterfly's repopulation. The Necedah National Wildlife Refuge in central Wisconsin is home to the world's largest population of Karner blues, which benefit from its vast area of savanna and extensive lupine.
In 2003, the Canadian Species at Risk Act listed the Karner blue as being extirpated from Canada. In 2012, after an unusually hot and dry year, the Karner blue was also extirpated in the Indiana Dunes National Park.
Description
alt=Female Karner blue butterfly nectaring on a flower; photographed in Concord, New Hampshire 2024.|230px|thumb|left|Female Karner blue nectaring on a flower in Concord, New Hampshire; note the orange crescents on the hind wing indicating sex
The male and female of this small (wingspan of about one inch) butterfly are different in appearance. The topside of the male is silvery or dark blue with narrow black margins. The female is grayish brown, especially on the outer portions of the wings, to blue on the topside, with irregular bands of orange crescents inside the narrow black border. The underside of both sexes is gray with a continuous band of orange crescents along the edges of both wings and with scattered black spots circled with white.
Distribution and habitat
The Karner blue butterfly occurs in portions of eastern Minnesota, Wisconsin, Michigan, and New York. Reintroductions have been initiated in Ohio, Indiana, Illinois and New Hampshire. The Karner blue butterfly appears extirpated from Iowa, Pennsylvania, Massachusetts, Maine, and Ontario in Canada.
Wild lupine
Several studies have found a positive relationship between measures of wild lupine and Karner blue butterfly abundance. However, available evidence suggests that senescent wild lupine is a poor larval food source. The effects of other phenological stages are more ambiguous. In west-central Wisconsin, Karner blue butterfly abundance was negatively associated with the abundance of reproductive lupine and positively related with the frequency of immature wild lupine. However, a feeding trial found that Karner blue butterfly fed 1st year wild lupine had one of the lowest survival rates observed and significantly longer larval durations than larvae fed older wild lupine that did not flower, was flowering, had recently flowered, or was grown in shade and was in seed. In addition, on sites in Wisconsin and Minnesota, the number of 1st flight oviposition sites on nonreproductive and reproductive wild lupine was similar. In addition, larval length was positively associated with wild lupine height in central Wisconsin. Higher nitrogen concentrations in wild lupine leaves resulted in significantly shorter larval durations in a feeding trial. In 1995, in west-central Wisconsin, significantly more Karner blue butterfly larvae were observed in oak-pine barren plots where mildew infection was delayed compared to areas where wild lupine were infected earlier. However, in a feeding trial larval duration of Karner blue butterflies fed mildew-infected wild lupine was not significantly different from treatments that resulted in the shortest larval durations. Karner blue butterfly fed water-stressed wild lupine had significantly longer larval durations than many treatments including larvae fed flowering wild lupine, shade-grown wild lupine in seed, or mildew-infected wild lupine. Shade-grown wild lupine being more nutritious, possibly due to nitrogen content limiting photosynthesis to a greater extent in open areas, was one of several explanations. The size of wild lupine has been positively associated with Karner blue butterfly larval length In Michigan, more Karner blue butterflies were observed on sites with more nectaring plants, especially butterfly milkweed (Asclepias tuberosa). In addition, treatments such as cutting with or without herbicides, herbicide application alone, or mowing at varying intervals resulted in a significant (p<0.01) increase in the number and cover of nectar species. See section "Food habits" for species that Karner blue butterflies use as nectar sources.
Other habitat characteristics: Although Schweitzer
In west-central Wisconsin, the amount of Karner blue butterfly larval feeding damage increased with grass cover.
Disturbance
Karner blue butterflies may be associated with disturbance. Although results may have been biased by a significant (p=0.009) positive correlation (r=0.2173) between patch area and number of disturbances (such as burning, vehicle traffic, and thinning and clearing), patches in a right-of-way in west-central Wisconsin occupied by Karner blue butterflies had a greater frequency of disturbance than unoccupied patches (p≤0.0125).
Temperature
Karner blue butterflies are directly affected by temperature. A review suggests that the cover provided by snowpack protects Karner blue butterfly eggs from hatching prematurely or being overheated by direct sunlight. Therefore, short periods of continuous snow cover due to site conditions or mild winters could result in decreased occurrence or smaller populations of Karner blue butterflies.
Landscape effects
Karner blue butterflies are dependent on heterogeneous habitat as it provides the varied requirements of different Karner blue butterfly broods, sexes, and life stages over a wide range of environmental conditions. Research at Indiana Dunes National Park led to recommendations for canopy openings for adult males and nectaring of both sexes, as well as areas with 30-60% cover for ovipositing females. In west-central Wisconsin the importance of shaded habitat led to a recommendation that 20% to 40% of Karner blue butterfly habitat provide shaded lupine and that 1/3 have >60% canopy cover with succession in these dense areas allowed to progress to complete closure. Maxwell In addition, wild lupine patches in the Allegan State Game Area that were occupied by Karner blue butterflies were closer to other occupied patches than wild lupine patches without Karner blue butterflies. This led to the recommendation that habitat patches be within of each other. Paper wasps (Polistes spp.), spined soldier bugs, and ants (Formica spp.) have been observed removing larvae, and the ant Monomorium emarginatum has been seen chewing on Karner blue butterfly eggs.
Mutualism with ants
Karner blue butterfly larvae benefit from a facultative, mutualistic relationship with several ant species. In pitch pine-bear oak (Pinus rigida-Quercus ilicifolia) habitat in New York, significantly more larvae tended by ants survived (67%) than untended larvae (38%). The 19 ant species tending Karner blue butterfly larvae were from the subfamilies Formicinae, Myrmicinae, and Dolichoderinae, which are the most common in the area. The species of ant is likely to influence the degree of benefit gained by Karner blue butterfly larvae. summarized the status of Karner blue butterfly across its range. Recovery criteria were addressed, discussed lessons learned while developing a statewide Habitat Conservation Plan for Wisconsin.
In 2023, the National Park Service published a 154-page report, using studies and recommendations that were motivated by population extirpations attributed to the 2012 drought and warmth that were regarded as a harbinger of more such events forthcoming owing to climate change. Among the recommendations were managed relocation of populations from the southern parts of its range into northward habitats with suitable conditions and supportive plants. The report supported this proposal by noting that stakeholders and managers "are growing more supportive of novel science-based interventions to save rare species from climate change—driven extirpation."
Articles that address Karner blue butterfly sampling methodology include. Swengel to suggest calculating male and female population sizes separately. General descriptions of Karner blue butterfly rearing methods and translocation/ reintroduction techniques are available.
A wide variety of management techniques can be compatible with maintaining Karner blue butterfly populations when attention is paid to implementing them at appropriate times and at intensities, scales, and frequencies that Karner blue butterflies can tolerate. For example, mowing can maintain open areas with little to no detrimental effect on Karner blue butterflies on sites where burning is impractical or in areas too small to support populations of Karner blue butterflies likely to survive a burn. On restored oak savanna sites in south-central Wisconsin, no significant (p=0.924) differences were detected between Karner blue butterfly densities on sites burned in summer, sites mowed in August, and control sites. Mowing with a blade height > should be performed annually or biennially in the fall or winter and clippings should be left in place. Information on the impacts of an insecticide on Karner blue butterflies and some herbicides on Karner blue butterflies as well as lupine and nectar species are available. According to the Karner blue butterfly recovery plan, management activities that can have a detrimental effect should be timed to allow at least 2 generations between repeat treatments and, if possible, critical subpopulations should be divided into discrete management units. Planting nonnative nectar sources is discouraged due to their potential impacts on native food sources, especially wild lupine.