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A loss of habitat and a favorite food has caused a tremendous decline in the Karner blue butterfly population, found at Indiana Dunes National Lakeshore. |
Butterflies are beautiful by nature. Their lavish colors are nearly intoxicating. Unfortunately, like many beneficial insect populations, some butterflies, including the Karner blue, are on the decline.
In the past century, the number of Karner blue butterflies has dropped about 95 percent. More than 90 percent of the decline has occurred in the last 15 years. The Karner population, which once occurred in a continuous narrow band across 12 states and Ontario, Canada, mostly has been relegated to Wisconsin, Indiana Dunes National Lakeshore, and Michigan. Remnants of the species, native to the Great Lakes region, also can be found in small sections of Minnesota, New Hampshire, and New York.
Although rough estimates put Indiana Dunes' Karner blue population somewhere between 10,000 and 15,000, Randy Knutson, a wildlife biologist at the park, emphasizes that the high figure in no way means that the butterfly is not a threatened species. He says that the butterflies have completely disappeared from areas where they were once prevalent and that at Indiana Dunes "one wildfire or drought could possibly do them in." He adds, "The park is a small, isolated island, and with very few butterflies around, [Karners] wouldn't be able to repopulate unless humans physically restored them."
The Karner blue is a small, sexually dimorphic butterfly. It has approximately a one-inch wingspan. The upper side of the male's wings are violet blue with black margins and fringed white edges. The female's upper side ranges in color from bright purplish-blue near the body to a dark grayish-brown with orange crescents on its edges and back wings. Both males and females have fawn-colored undersides with speckled orange and metallic spots on all four wings.
Two batches of Karner eggs hatch each year. In April, the first group of caterpillars hatch from eggs laid the previous year. The caterpillars pupate by mid-May, and adult butterflies emerge from cocoons in June. These adults mate and lay their eggs on or near wild lupine plants. After seven days, the eggs hatch and the caterpillars feed for the next few weeks. The summer's second generation of adults appears in July. The Karner takes flight only twice during the summer.
The butterfly's ability to reproduce depends largely on wild lupine plants, which require dry soils in open to partially shaded woods and clearings, such as oak savanna, to survive. Although adult Karner blues feed on the nectar of various flowering plants, the caterpillars feed only on the wild lupine's leaves, making the plant critical to the butterfly's survival.
Decades of wildfire suppression have affected the butterfly's habitat. Without fire or other disturbance activities such as grazing, shrubs and trees invade open savanna and barrens and shade out grass and herbaceous plants, making it difficult to find lupine. Limited habitat often results in small, isolated Karner populations unable to adapt to environmental changes. Clearing land for farming and commercial and residential development also contribute to the Karner's waning numbers.
Indiana Dunes, however, is clearing some trees by using prescribed fires and other methods such as timber harvests to improve habitat for the butterfly. Knutson says the park plans to help restore the Karner to its natural range.
Although it's difficult to say whether the Karner blue butterfly will ever become de-listed, Knutson is optimistic about the insect's future. If the federal recovery plan, still in draft form, is adhered to, Knutson says, "there's a good possibility of that happening."
Jenell Talley is publications coordinator.
