They are found in the midwestern and northeastern parts of the United States. Many people like to collect Karner Blue butterflies because they are so beautiful. However, because numbers of Karner Blue butterflies are so low, the collection of even a few can seriously harm their population. An even bigger problem for these butterflies is habitat loss. The only known food of the Karner blue butterfly is the wild lupine, a small blue flowering plant.
Wild lupine grows best in sandy soils, in areas that are occasionally cleared by wildfires.
Land development and lack of wildfire have reduced the growth of this plant. Without the wild lupine, Karner Blue butterflies cannot exist.