As the first North American insect to go extinct due to humans, a blue butterfly has become an icon for insect conservation -- and what happens when humans destroy habitats without thought for the animals living in them. The last of the Xerces blue butterflies fluttered through the air in San Francisco in the early 1940s. Now, they can only be seen in glass displays at museums. These periwinkle pearly-winged insects lived in the coastal sand dunes along San Francisco and were first characterised by scientists in 1852. When urban development swept through this part of California, the sandy soils were disturbed. This caused a ripple effect, wiping out species of the plant the Xerces caterpillars used. The habitat change was too great for the Xerces blue butterfly, and the species went extinct.