Plebejus melissa samuelis (Nabokov, 1944)
Karner Blue
MN Status:
(as Lycaeides melissa samuelis)
Federal Status:
CITES:
USFS:
Habitats:
(Mouse over a habitat for definition)
Lycaeides melissa samuelis
Basis for Listing
The historical range of the Karner blue forms a narrow band from Maine and New Jersey westward through the southern Great Lakes region to eastern Minnesota and northeastern Iowa (Dirig 1994). It was always a highly local species because of the naturally patchy distribution of its specialized habitat, sandy barrens and savannas where its obligate larval host plant, wild blue lupine (Lupinus perennis), occurs. Human land use has had a severe impact on this habitat, resulting in the disappearance of many colonies and the reduction of most others to precariously small numbers of adult butterflies. The Karner blue is believed to be extirpated in several states and the Province of Ontario, and is barely hanging on in several others (NatureServe 2008). Only in Wisconsin are there still numerous colonies, including several sizeable metapopulations (Bleser 1994).
Appropriate habitat for the Karner blue was limited in Minnesota even before Euroamerican settlement. Wild blue lupine reaches the western limit of its range in central Minnesota, and within this range its occurrences were always very discontinuous, reflecting the distribution of large sand deposits. Development and succession of savanna to closed woodland and forest following fire suppression have eliminated many wild blue lupine populations or reduced them to small numbers of plants in scattered openings. The Karner blue was not discovered in Minnesota until 1975, making its pre settlement status here purely speculative. It has been confirmed at only two locations in the state, one in the southeast closest to the large central Wisconsin concentration of occurrences, and one in the east-central part of the state closest to the northwest Wisconsin population. The latter site supported a very small colony at the time of its discovery and died out in the 1980s. The former, although it comprises a number of habitat patches, has consistently produced small numbers of butterflies (Lane and Dana 1994). Searches of all other known potential habitat have failed to find the Karner blue (Cuthrell 1990; R. Dana, Minnesota DNR, pers. comm.). The Karner blue was orginally listed as a threatened species in Minnesota in 1984 but due to its extreme rarity in the state, it was reclassified as endangered in 1996. It has been federally listed as endangered by the U.S. Fish and Wildlife Service since 1992.
The Karner blue is a typical member of the subfamily of the Lycaenidae commonly known as blues because of the blue coloration of the upper wing surfaces in males (females usually are more brown than blue). It is a small butterfly (forewing length 1.2-1.5 cm (0.47-0.59 in.) from base to apex) with rounded wings. Males and females are nearly identical in size and shape. The dorsal surfaces of both hind and forewings of males are bright, violet- or lilac-tinged blue, with a slight frosting of whiter scales in fresh individuals, especially along the veins. There is a thin black line along the outer edge of the wings, and a contrasting fringe of long, white scales. The thorax above is clothed in a dense pile of blue hairlike scales. The female is mostly dark brown above, with blue scaling confined to the basal area of the wings. There is a row of circular black spots near the outer margin of the hind wing that are capped on their inner sides with bright orange crescents. Beneath, the sexes are nearly identical, with a sparse pattern of white-ringed black spots on a pale gray ground (sometimes darker gray in females). Near the outer margin of the hind wing there is a band of prominent, bright orange crescents each enfolding a silvery-blue eye and thinly capped on the inner edge with black. Smaller orange spots without the silvery inclusions continue the band along the forewing.
There are several other blues in Minnesota that might be mistaken for the Karner blue. Most similar is the melissa blue (Lycaeides melissa melissa). Males are virtually indistinguishable, but females of the melissa blue have the orange crescents on the upper hind wing enlarged and nearly fused into a continuous band, and this band continues along the outer edge of the forewing. The basal blue scaling is also greatly reduced compared with the Karner blue, or, more typically, absent. The melissa blue occurs commonly in the prairie part of Minnesota, west of the range of the Karner blue, but several colonies have recently been discovered within the Karner's range. Nabokov's blue (L. idas nabokovi) is also quite similar. Again, males are extremely difficult to separate. Typically the orange markings on the lower surfaces of the wings are smaller in Nabokov's than in the Karner, but genitalic dissection is needed for confident determination. Females have at most only traces of orange on the upper hind wing. Nabokov's blue occurs in the northern forested part of Minnesota. The eastern tailed blue (Everes comyntas) is smaller than the Karner blue and has a tiny threadlike tail on each hind wing. The orange spots on the hind wing are small and only two are usually present. Other blues that are likely to be encountered within the Minnesota range of the Karner blue lack any orange markings at all. These include the silvery blue (Glaucopsyche lygdamus), the spring azure (Celastrina ladon), and the summer azure (C. neglecta).
Minnesota's only surviving occurrence of the Karner Blue butterfly is in a mosaic of oak savanna and sand barrens habitats in the southeast, where wild blue lupine is common. The extirpated colony was concentrated along an unpaved township road through an overgrown sand savanna. Although wild blue lupine plants could still be found in the overgrown savannah away from the road, the butterfly utilized primarily a small population of vigorous plants along the road edges (Lane and Dana 1994). Similar habitats are reported for Wisconsin and Michigan (Swengel and Swengel 1997; Nielsen 1999).
Biology / Life History
The Karner blue has two generations each year throughout its range, including Minnesota. Eggs laid by the second generation females overwinter and hatch early in the spring. Although the eggs are laid on various plant surfaces near the bases of wild blue lupine plants, the tiny hatchling larvae have to find their way to lupine shoots emerging from the soil. The first generation adults can begin to appear in mid-May and are mostly gone by late June. Year-to-year variation in the rate of warm-up can advance or retard the flight period. Females of the first generation lay their eggs on lupine stems and leaves. Second generation adults emerge and fly beginning as early as mid-July and continuing into late August. Adult life expectancy in the wild is estimated to be only a few days. There is no information on how many eggs a female will lay over her lifetime.
Wild blue lupine is the only known larval host plant throughout the range of this butterfly. Larvae feed on leaves and to some extent also on developing fruits (R. Dana, Minnesota DNR, pers. comm.). Larval feeding creates characteristic window-paning or shot holes in leaves. Larvae are attended by ants, especially large Formica species that react aggressively to potential predators approaching the larvae (Savignano 1994; R. Dana, Minnesota DNR, pers. comm.). Like many lycaenid butterflies, Karner blue larvae have a specialized organ for producing a sweet liquid avidly fed on by ants and other organs that produce mimics of ant pheremones to further manipulate ant behavior (Malicky 1970). This ant association helps protect larvae from natural enemies (Savignano 1994). Larvae rest on the wild blue lupine plants when not feeding, and pupate primarily in leaf litter (Lane 1999). Adults of both sexes visit flowers for nectar, and males also imbibe from animal dung and moist sand.
Males seek receptive females primarily by flying about lupine patches searching for them, although they will also pursue as potential mates insects that fly nearby while they are resting or basking. Other Karner blue males are the most frequent object of such chases. Nothing is known about female remating frequency. Dispersal behavior is poorly understood. Most observers have reported that adults tend to remain within small areas, but a few studies have suggested that longer-distance dispersal events (1.5-2 km; 0.9-1.2 mi.) may not be rare (U.S. Fish and Wildlife Service 2003). What conditions are barriers to movement among habitat patches, and conversely, what conditions are conducive to movement, are mostly a matter of speculation.
Conservation / Management
The small size of Minnesota's only known colony is the primary threat facing the Karner blue in the state. Such a small, isolated colony is at high risk of extirpation resulting from both natural events (such as severe drought or hailstorms) and human caused ones (such as insecticide application), as well as from the vagaries of normal population processes (for example, by chance all adults in one generation are males). Loss of genetic diversity in a small population is another possible threat. The Minnesota colony is at least 80 km (48 mi.) from the nearest known occurrences in Wisconsin (Eau Claire and Jackson counties), making it unlikely that immigration from the Wisconsin population will maintain genetic diversity.
The possible fragmentation of this small colony into even smaller units confined to the separate patches of suitable habitat aggravates the risk of extirpation. Fire suppression has allowed the original oak scrub and woodland matrix to grow up into dense woodland and forest that probably impedes butterfly movement among the patches, and even these have been shrinking as oaks invade. The Karner blue is probably highly susceptible to fire, as eggs or small larvae that would be the exposed stages during the times most management burning is done exhibit no obvious adaptations that would shield them from lethal temperatures (Swengel 1994). However, wild blue lupine responds to dormant season fire with vigorous growth, and the butterfly quickly recolonizes burned areas if there are adults available (Swengel 1994). Therefore, burn units and rotations should be designed to insure that adults will be available to recolonize and that enough time elapses between burns for numbers to rebound. Mechanical clearing is an option where fire would be risky, but the long term suitability of areas managed exclusively with mechanical clearing is unknown. Opening up woodland and forest between patches to provide greater connectivity can be done at little or no risk to the butterflies.
The gypsy moth (Lymantria dispar) will soon invade the area where the Karner blue occurs in Minnesota. The oak-dominated woodlands and forests here are prime candidates for defoliating outbreaks, and there will be considerable pressure to control gypsy moth numbers with insecticides. Two products used for this purpose are diflubenzuron (Dimilin) and the toxin derived from the bacterium Bacillus thuringiensis var. kurstaki (Btk). The latter is known to be highly toxic to Karner blue larvae (Herms et al. 1997), and the former, which disrupts molting in insects, is almost certainly as toxic to the Karner blue as it is to the gypsy moth. It will be imperative to keep application of either of these products well away from Karner blue habitat.
Recently discovered colonies of the melissa blue in eastern Minnesota and western Wisconsin that are using introduced legumes, alfalfa (Medicago sativa) and crown vetch (Coronilla varia), as larval hosts pose a new threat. Both legumes are widely planted within the Karner blue's range, creating the opportunity for the melissa blue to invade and hybridize with the Karner blue. This could lead to the eventual disappearance of the Karner blue. Recent molecular studies have found that genetic differentiation between these two taxa is very weak (Packer et al. 1998; Nice et al. 2000), suggesting that hybridization will be likely and that offspring of hybrids and backcrosses will be viable.
Conservation Efforts in Minnesota
In September 2003, the U.S. Fish and Wildlife Service completed a national Karner blue butterfly recovery plan. The objective of the plan is to restore viable metapopulations of Karner blues across the species extant range so that it can be reclassified from endangered to threatened, and eventually removed from the federal endangered species list altogether.
All of the known habitat occupied by the Karner blue in Minnesota is within a DNR Wildlife Management Area and there is an ongoing research and management effort on behalf of the butterfly at this site (see video). Fire and mechanical clearing have been used to improve existing habitat and to open up overgrown potential habitat. The Minnesota DNR also monitors butterfly abundance at this site annually. There are few other known occurrences of habitat suitable for the Karner blue in Minnesota. Suitable habitat areas were surveyed in 1990 by the Minnesota DNR (Cuthrell 1990), and the butterfly was only found at the one location. The other sites have also been visited one or more times by other experienced lepidopterists with the same results.
References and Additional Information
Bleser, C. A. 1994. Karner Blue Butterfly survey, management and monitoring activities in Wisconsin: 1990-Spring 1992. Pages 153-162 in D. A. Andow, R. J. Baker, and C. P. Lane, editors. Karner Blue Butterfly: a symbol of a vanishing landscape. Miscellaneous Publication 84-1994, Minnesota Agricultural Experiment Station, University of Minnesota, St. Paul, Minnesota.
Cuthrell, D. L. 1990. Status of the Karner Blue Butterfly, Lycaeides melissa samuelis Nabokov, in Minnesota 1990. Report submitted to the Nongame Wildlife Program, Minnesota Department of Natural Resources. 44 pp. + appendix.
Dirig, R. 1994. Historical notes on Wild Lupine and the Karner Blue Butterfly at the Albany Pine Bush, New York. Pages 23-36 in D. A. Andow, R. J. Baker, and C. P. Lane, editors. Karner Blue Butterfly: a symbol of a vanishing landscape. Miscellaneous Publication 84-1994, Minnesota Agricultural Experiment Station, University of Minnesota, St. Paul, Minnesota.
Herms, C. P., D. G. McCullough, L. S. Bauer, R. A. Haack, D. L. Miller, and N. R. Dubois. 1997. Susceptibility of the endangered Karner Blue Butterfly (Lepidoptera: Lycaenidae) to Bacillus thuringiensis var. kurstaki used for gypsy moth suppression in Michigan. The Great Lakes Entomologist 30:125-141.
Lane, C., and R. Dana. 1994. The status of the Karner Blue Butterfly in Minnesota. Pages 113-122 in D. A. Andow, R. J. Baker, and C. P. Lane, editors. Karner Blue Butterfly: a symbol of a vanishing landscape. Miscellaneous Publication 84-1994, Minnesota Agricultural Experiment Station, University of Minnesota, St. Paul, Minnesota.
Lane, C. P. 1999. Benefits of heterogeneous habitat: oviposition preference and immature performance of Lycaeides melissa samuelis Nabokov (Lepidoptera: Lycaenidae). Dissertation, University of Minnesota, St. Paul, Minnesota. 185 pp.
Malicky, H. 1970. New aspects on the association between lycaenid larvae (Lycaenidae) and ants (Formicidae, Hymenoptera). Journal of the Lepidopterists' Society 24:190-202.
NatureServe. 2008. NatureServe Explorer: An online encyclopedia of life [web application]. Version 7.0. NatureServe, Arlington, Virginia. . Accessed 3 June 2008.
Nice, C. C., G. Gelembiuk, N. Anthony, and R. ffrench-Constant. 2000. Population genetics and phylogeography of the butterfly genus Lycaeides. April 21, 2000 report to U.S. Fish and Wildlife Service, Fort Snelling, Minnesota. 43 pp.
Nielsen, M. C. 1999. Michigan butterflies and skippers: a field guide and reference. Michigan State University Extension, East Lansing, Michigan. 248 pp.
Packer, L., J. S. Taylor, D. A. Savignano, C. A. Bleser, C. P. Lane, and L. A. Sommers. 1998. Population biology of an endangered butterfly, Lycaeides melissa samuelis (Lepidoptera: Lycaenidae): genetic variation, gene flow, and taxonomic status. Canadian Journal of Zoology 76:320-329.
Savignano, D. A. 1994. Benefits to Karner Blue Butterfly larvae from association with ants. Pages 37-46 in D. A. Andow, R. J. Baker, and C. P. Lane, editors. Karner Blue Butterfly: a symbol of a vanishing landscape. Miscellaneous Publication 84-1994, Minnesota Agricultural Experiment Station, University of Minnesota, St. Paul, Minnesota.
Swengel, A. B. 1994. Observations on the effects of fire on Karner Blue Butterflies. Pages 37-46 in D. A. Andow, R. J. Baker, and C. P. Lane, editors. Karner Blue Butterfly: a symbol of a vanishing landscape. Miscellaneous Publication 84-1994, Minnesota Agricultural Experiment Station, University of Minnesota, St. Paul, Minnesota.
Swengel, A. B., and S. R. Swengel. 1997. Co-occurrence of prairie and barrens butterflies: applications to ecosystem conservation. Journal of Insect Conservation 1:131-144.
U.S. Fish and Wildlife Service. 2003. Final Recovery Plan for the Karner Blue Butterfly (Lycaeides melissa samuelis). U.S. Fish and Wildlife Service, Fort Snelling, Minnesota. 273 pp.