Saturday, August 13, 2016

Red-spotted Purple

RSP - Belle
My 10 year old naturalist friend Belle sent me this photograph of a Red-spotted Purple (RSP) butterfly that reminded me of a past exploration into the caterpillars.  The RSP, Limenitis arthemis astyanax, is a forest butterfly that is well adapted to suburban areas with trees.  In flight it resembles Pipevine and Spicebush Swallowtail butterflies, a protective coloration called Batesian mimicry as a bird having tasted one of those toxic species is likely to leave the RSP alone.

Viceroy - Wikipedia
The RSP has an unusual trait of occasionally mating with the closely related Viceroy butterfly Limenitis archippus, usually in the lab but occasionally in the wild.  One definition of a species is their ability to breed so once again the definition of species is challenging.
RSP or Viceroy? - REK
Since the two species are close enough that they occasionally interbreed, it probably should not be a surprise us that their larvae can look similar.   They are the only bird dropping mimic caterpillars that have horns. The RSP is less spiny than the Viceroy.  I photographed the caterpillar above from many angles and yet we were never able to decide which species it was.  Only the mother knows for sure.

Southern Viceroy - Mark Fox
RSP - Carmen Champagne CC

Bird dropping mimic with horns - REK

The RSP rarely feeds on nectar from flowers, preferring fermenting fruit that is "spoiling" for us but tasty for it, tree sap and even animal dung.  They also will drink from moist gravel and mud puddles, acquiring the minerals they need for reproduction.

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