Tuesday, March 29, 2011

Red-spotted Purple intergrade

As I continue my digital butterfly search about which I previously blogged, I came upon this photo taken on 25 June 2007 on one of Erika's garden hostas in Northfield.  The butterfly appears to be an intergrade between a White Admiral and a Red-spotted Purple.  The Canadian admiral barely trespasses into the northern United States.  The purple is found in the eastern US and in Mexico.  The two butterflies have different habitats--the White Admiral is more restricted to forests, whereas the Red-spotted Purple prefers open, scrubby woods and forest edges (Klots).  My butterfly was along the forest edge.

Despite being quite different in appearance, where their ranges overlap (in Minnesota, Michigan, and New England), you encounter intergrades.  The admiral shows broad white wing stripes; the purple lacks the stripes and is purple and blue.  Klots (A Field Guide to the Butterflies) and Marrone (Field Guide to Butterflies of South Dakota) show intergrades with a lot of white on the upper wing. The intergrade shown in Kaufman (Butterflies of North America) looks similar the butterfly in my photo. Once considered to be two separate species, this hybridization forced lepidopterists to conclude that we are dealing with one polymorphic species.

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