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The Karner Blue Butterfly
The Karner Blue Butterfly
January 31, 1996
In 1992 the Fish and Wildlife Service listed the Karner blue butterfly as an endangered species. Although now considered rare and declining in numbers, the butterfly was once common. Habitat destruction due to development is commonly blamed for the decline of the butterfly. Ironically, however, human intervention in the environment may also provide the opportunity to save the Karner blue.
In 1861, William Saunders of Ontario caught the first Karner Blue specimen. At the time there were scores of thriving populations from southern Minnesota all the way to New Hampshire. Saunders sent his specimen to William Henry Edwards of Philadelphia, who assigned it to the species Lycaena scuderii, Scudder's blue. The butterfly was later called the Karner blue because of the area where it had first been collected and described.
The Karner blue is an inconspicuous butterfly. The butterflies have a wingspan of approximately one inch and with their wings folded they appear to be a rather plain slate gray. Only when their wings unfold do the males show the silvery blue markings on the backs of their wings that give them their name.
Usually, the Karner blue butterfly has two broods each year. Eggs that have overwintered from the previous year hatch in April. The larvae feed on wild lupine leaves and mature rapidly. Near the end of May, they pupate and adult butterflies emerge. The adults are in flight for the first two weeks of June when the wild lupine is in bloom. Females lay eggs on or near the wild lupine plants, after which the females soon die. The summer eggs hatch in about a week. The emergent larvae feed on the lupine for three weeks, pupate and the second (summer) brood adults appear in the second or third week of July. This time eggs are laid among the plant litter, on or near lupine plants. By early August all adults have died and the eggs winter over.
In 1941, writer Vladimir Nabokov, who happened to be an amateur lepidopterist of considerable stature, received a non-paying curatorial position at the Harvard Museum of Comparative Zoology. Nabokov decided to sort out the North American members of the genus Lycaeides, which had previously been classified in several mutually contradictory schemes. In the course of his work Nabokov determined that the Karner blue was not of the species L. scuderii, but was in fact a subspecies of Lycaeides melissa. Nabokov renamed the butterfly Lycaeides melissa samuelis in honor of the entomologist Samuel Scudder for whom the butterfly had previously been named.
The habitat of the Karner blue is characterized by the presence of wild lupine (Lupinus perennis), a member of the pea family. Wild lupine is the only known food source for larva of the butterfly. Consequently, the butterfly is wholly dependent on the presence of lupine for its survival.
Lupine is an early successional plant. As fire or some other disturbance sweeps across a forest landscape destroying vegetation, lupine moves in to take advantage of the sunlight afforded by the burned or disturbed land. It will flourish for several years until bushes or trees provide too much shade for it to grow and blossom.
Repeated burning by native Americans followed by land clearing by early settlers historically insured an abundant lupine population. Fire suppression in recent decades combined with the return of higher successional forests have depleted the lupine, and consequently the butterfly as well. The only places lupine is consistently found is in poor soil conditions such as pine barrens where the soil is too poor to allow dense undergrowth.
The range of lupine extends from Maine, south to Florida and as far west as Louisiana and Minnesota. The butterfly inhabits only a narrow band in the Northern portion of the lupine's range. Historically it ranged from New England, through the Great Lakes region and into Minnesota.
Because lupine is a transitory plant, conservation of the butterfly necessitates a solution other than a conventional regulatory strategy. Areas which have been disturbed and contain the butterfly, if left alone, will slowly become non-butterfly habitat. The most areas where lupine currently exists, such as pine barrens, cannot indefinitely support a stable population of butterflies. In other words, without active human involvement the butterfly is likely to face extinction in the long term.
The Karner blue is now found in only a handful of sites and has been extirpated in Massachusetts, Pennsylvania, Ohio, Iowa, Illinois and Ontario. The remaining populations are highly scattered and colonies rarely exceed 1,000 individuals. Such small and disperse colonies are highly vulnerable to weather events. The extinction of Karner blue butterflies in Ontario exemplifies this. In 1984, the population of butterflies in Ontario was estimated to be approximately 1,000 adults. The drought of 1988, followed by unusually cold weather in May and June of 1989, killed off the Karner blue butterflies. None have been seen in Canada since 1989.
The only colony in the world which has significantly more than 1,000 adult butterflies is the population found at the Saratoga County Airport. In fact, half the world population of Karner blue butterflies is found in this one location, with an estimated 14,000 adults. Ironically, the habitat at the airport is not considered natural. The lupine likely invaded the area when it was disturbed and has been maintained by constant human intervention. This single largest population and habitat for the butterfly is a fake sand-prairie in a region where there have been no sand prairies for tens of thousands of years, an irony which has been noted by some of the butterfly's researchers. Some researchers have even suggested that the fake prairie is a better habitat for the Karner blue than many prairie preserves.
The occurrence of butterflies at the Saratoga airport is something of a chance coincidence. The airport was likely created out of previously cultivated land. As annual plowing and planting ceased, local wild flowers exploited this new landscape, just as if this area had been burned by a fire. One of these wild flowers is lupine. This keeps out trees and enhances visibility. It takes relatively little mowing to keep trees and large bushes to a minimum, simply mowing once a year is usually sufficient. This sort of annual mowing keeps the area in a state of perpetual early succession.
This fake prairie may be a better for the Karner blue butterfly than natural prairie preserves because of fire. Fire historically created the prairie and oak savanna habitat in which the lupine thrives. Lupine has a long tap-root which extends several feet into the earth. In a fire the lupine leaves and stems will burn but the root is protected by the insulating soil. Once the fire is over, the plant sends up new shoots from it's tap root. Although lupine is well adapted to coping with fire, the butterfly is not. Fire kills the butterfly. Any eggs, larva, pupae or adult butterflies in a fire's path will be destroyed.
A large prairie preserve could be managed with fire without unduly endangering the butterfly. But in a small preserve, such as those surrounding most of the butterfly populations, the butterflies will be destroyed unless extreme care is taken. Management by fire ultimately means that the butterfly is constantly faced with population setbacks.
Mowing, however, does not have to kill the butterfly. The eggs which survive the winter are generally laid in the leaf litter or near the base of lupine plants. Mowing conducted after the butterflies have laid their eggs, sometime in September would have little effect on next springs butterfly population. This is reflected in the mowing schedule followed by the Saratoga county airport, which is surprisingly simple. After September every year, the area is mowed to a height of eight inches.
Population studies of the Karner blue have shown that one of the critical factors in its survival is the number of healthy lupine plants in the spring when the over wintering eggs hatch. A survey of thirty seven sites conducted in 1980 in New York revealed that on average two plants of lupine are required to support every caterpillar.
In addition to lupine, adult butterflies which emerge in July need nectar bearing plants on which to feed. Lupine blooms in June and nectar from the flowers feeds the first brood of adults. Lupine, however, is not flowering in late July and the butterfly must use other plants as a source of nectar. Literature suggests that butterfly weed is the preferred secondary nectar source for Karner blue butterflies, however there are a number of other flowers the butterfly can use as a nectar source.
As with the airport in Saratoga county, there are certain human activities which are constantly creating an early successional habitat. For example, utility companies keep the right-of-way around their power transmission lines constantly mowed. This effectively creates thousands of miles of early succession habitat, albeit in narrow strips. In addition, there are thousands of airports in the former range of the butterfly. In essence, any patch of land from Maine to Minnesota which is mowed only to keep out trees is potential butterfly habitat.
Wild lupine seed and plants are readily available from several seed companies and nurseries and could easily be planted. Such areas as right-of-ways and airports could provide the ideal habitat for the butterfly. In fact lupine may already exist in some stretches of right-of-way. Planting lupine and adjusting mowing schedules could ensure a continuous habitat of lupine for the butterfly. Once the lupine has been established, butterfly cocoons, lupine plants with butterfly eggs, or adult butterflies could be introduced. Normally private land owners would be reluctant to allow an endangered species to be intentionally introduced onto their land. However, the existing statute contains exceptions for experimental populations. Experimental populations do not have the same status under the act granted to wild populations. The butterflies should only be introduced if the Fish and Wildlife Service is willing to designate them an experimental population and exempt them from the regulatory provisions of the act.
Once established it is quite possible that the lupine will not only thrive but also spread. Established experimental populations of butterfly should also spread with the lupine.
The ease with which a large population of Karner blue butterflies is maintain at the Saratoga county airport suggests that private conservation efforts if properly executed could be enormously successful in enhancing the population of the butterfly.
This case study was written by Jonathan Tolman, an environmental policy analyst at the Competitive Enterprise Institute.