Red-spotted Purple caterpillar. (Photos by Kay Fairweather)
Name: The Red-spotted Purple is a large colorful butterfly with the scientific name Limenitis arthemis astyanax. It is a member of the “brush-footed” butterfly family which has about 3,000 species worldwide and includes the Admirals, Checkerspots and Painted Ladies. The common factor shared by all the members is that the first pair of legs is much reduced and they are also hairy, hence the name brush-footed. The red spots are more orange than red and there isn’t really any purple on the butterfly. It could have been named by the same person who named the White Admiral, aka the Banded Purple, which is neither white nor purple. Lepidopterists now consider the White Admiral and the Red-spotted Purple to be the same species – just with different colors. The caterpillars look similar but the adult butterflies are markedly different. They are known to inter-breed. The name for the White Admiral used to be Basilarchia arthemis and the Red-spotted Purple was Basilarchia astyanax. If you have an older book, you will find them under those names. In newer books, they have the genus name, Limenitis.
When and where seen: My encounter with this butterfly started in the caterpillar stage of its life. I was walking in the Estabrook woods on May 6 with Leslie Thomas when she noticed a caterpillar crawling on her shirt. Neither of us had seen one like it before and I took it home for care and feeding until it became a butterfly. The first task was to identify the caterpillar so I would know what to feed it. I was able to identify it and discover that some of its common food plants are cherry, oak, willow and poplar. It was uninterested in any of the leaves I offered it and by May 8 it had fixed itself upsidedown to the wall of the container I had it in. Its legs pulled in, its horns disappeared, the exoskelton of its face fell off, and it shrivelled into a chrysalis about half the size of the caterpillar. On May 21 the butterfly emerged and I let it fly away. This species has two generations in a year so you are likely to see it in either its adult form or again in July and August as a caterpillar.
Mimicry: The Red-spotted Purple uses mimicry at all stages of its lifecycle as a strategy against predation. The caterpillar mimics a bird dropping. It was about two inches long, lumpy and bumpy and a mix of white and yellowish-brown colors. Just behind the head it had a pair of “horns.” They were brown and seemed kind of fleshy, and the horns themselves had horns. The chrysalis looked even more like a bird dropping than the caterpillar.
The adult butterfly, when its wings are spread, mimics the Pipevine Swallowtail which birds have learned to avoid because of its toxicity. The Red-spotted doesn’t have the “tails” of the Pipevine Swallowtail but it is of a similar size (wingspan around three inches) and is black with a metallic blue sheen. There are a few brick red spots on the forewing and blue spots on the hind wing. The wing edges are scalloped. The red spots which give rise to its name are on the underside of both pairs of wings so you can see them when the wings are folded or the butterfly is in flight. The spots are more orange or brick-red than true red.
References: Robert Michael Pyle, Audubon Field Guide to North American Butterflies; David L. Wagner, Caterpillars of Eastern North America; there are good photos on Bug Guide at http://bugguide.net/node/view/38193
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