That's Not a Red Admiral. . . it's a Satyr Comma

As we were collecting more Red Admirals (Vanessa atalanta) today at Tilden Regional Park (Berkeley, CA), we also unexpectedly happened to find a Satyr Comma caterpillar (Polygonia satyrus) among them!

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Since 7/25's post about finding some Red Admiral caterpillars (Vanessa atalanta) for the first time, we have wholeheartedly decided to look for more the next time we go to Tilden. That was today; around 8 PM we headed back not only to pick pipevine leaves (Aristolochia californica) for our Pipevine Swallowtails (Battus philenor) but also to ransack the creek's stock of stinging nettles (Urtica dioica) for more goodies -- this time equipped with some (somewhat) protective gloves, scissors, and a pair of forceps.  

When we got there, the sun was just starting to set so it was hard to see very well like last time. We would have to act quickly if we hoped to search for Red Admiral caterpillars or eggs before it got dark. The first place we searched was a nettle plant growing next to the fence in the butterfly garden which is where we found the bulk of the six caterpillars last time. Searching techniques apply here: of the five or so nettle plants growing near and along the creek, this was the most exposed (out in the open, in the sun) and closest to the other plants in the butterfly garden (after all, it itself is growing in the garden) which provide adult nectar sources. Both of these factors make this particular nettle plant superior to the others for attracting ovipositing females (see our Lepidoptera Rearing Guide for more details). And sure enough, we found two more caterpillars on it and a total of 14 eggs, most of which looked and probably were freshly laid since we didn't notice them last time.

The other nettle plant in the butterfly garden was growing in a more concealed location in the shade and didn't have anything on it so our next stop was a plant growing next to the creek. Last time, we only noticed this one when it was getting dark and didn't get a very good chance to investigate it. This time, we painstakingly managed to scrape up three more caterpillars hidden among the leaves growing right on the edge of water (it was a brutally inconvenient location to be). The other two nettles were growing among the bramble (Rubus ursinus) under a canopy of trees and, at first glance, didn't appear to have any caterpillar nests on it so at that point we called it a day. 

When we got home and tallied our stock, we noticed some pretty interesting color variations among the five new caterpillars, as well as the six old ones. Not one of them looked exactly the same! Yesterday we had found four light morphs of varying shades of white, yellow, and even green as well as a brown one and a black one striped with yellow. Today we had found a pinkish brown one, a gray one, a brownish gray one striped with yellow, a pitch black one, and . . . a strange looking white one. Diverse color morphs within Vanessa caterpillars (as well as many other members of the Nymphalinae [subfamily of Nymphalidae]) is a well known occurrence and seems to be more or less random and up to genetics (though the younger instars do tend to be darker, and newborns are always black). Even the butterflies have been observed and shown experimentally to bear many different appearances based on both genetic and environmental factors. For example, cold shocking chrysalises immediately after pupation has been shown to create some pretty striking aberrations. But after pondering it for a while, we could come up with not good explanation as to what was up with the last white colored one other than that it was a different species. . .

No matter what color form the Red Admiral caterpillars possess, they always maintain a pitch black, somewhat rounded head capsule unless they suffer from some obscure genetic defect such as albinism. This white caterpillar had a very white head, allowing the markings to be clearly seen. In addition, the head capsule was more square-shaped rather than round, with angular corners. The top of the head was so angular it almost appeared to have small horns and looked quite similar to a heliconian (subfamily Heliconiinae) caterpillar's head like the Gulf Fritillary (Augraulis vanillae). And although the body looked incredibly similar to that of the other caterpillars and the size was roughly the same, we noticed that the branches on its spines were proportionally just a bit longer than the others', making it appear more hairy.

So many Nymphalinae look so similar that it can sometimes be a hassle to identify their caterpillars; it is no wonder why we initially mistook it as just another Red Admiral. At second glance though, it clearly appears to be a caterpillar of the Satyr Comma (Polygonia satyrus). The Satyr Comma is another Nymphalinae butterfly that inhabits a very similar niche as the Red Admiral. It too feeds almost exclusively on nettles (Urticaceae), builds leaf nests by pulling two leaves together with silk, and primarily inhabits riparian areas on the edges of wooded areas (such as where we found it at Tilden) that support the host plants. If the two species' range overlap in one area, it is not uncommon to see both of them flying at the same place at the same time. However, Tilden seems to currently being dominated by the Red Admiral based on our findings. . . that is assuming, of course, that we haven't also made a mistake in identifying some of the other caterpillars that we think must be Red Admirals!

- Brian