Gray Hairstreak (Strymon melinus) fed Coral Vine flowers

    caterpillar when found, 4-12-09           4-14-09, still eating original seed pod

4-16-09, munching on flowers one day after being given only Coral Vine

4-17 and 4-18-09, respectively: the color is definitely changing 

4-19-09, pink is much more apparent after molt

4-22-09, last instar

4-25-09, pupa of this caterpillar (right) is pinkish compared to the norm (left)

Last fall, Dan Hardy asked for identification of a hairstreak caterpillar that he had found feeding on Coral Vine (Antigonon leptopus) in Mexico [See TX-Butterfly Listserv archives, message #163 for October, 2008]. The caterpillar in question was surprisingly pink. Nick Grishin suggested it was a Gray Hairstreak, S. melinus. Ever since, I have wondered, could a normally green Gray Hairstreak caterpillar turn pink?

I recently had opportunity to answer that question. I was raising a Gray Hairstreak caterpillar for photographic study when I found another young one. I decided to try to convince the second caterpillar to eat Coral Vine flowers. I placed the caterpillar, on its original host plant, in a container with Coral Vine. After two days I removed the original seed pod and left only flowers. The caterpillar readily accepted the new food. The experiment was on.

Coral Vine has long chains of pink flowers. The caterpillar would bore a hole into the side of one flower, and then move on to another. I often would find it with head inside the flower and hind end sticking out. This appears to me to be a rather vulnerable position and may explain why few caterpillars are found eating Coral Vine! As can be seen from the pictures, the caterpillar definitely took on the color of the food plant. The beginning of the color change could be seen even on the second day after the caterpillar began eating the flowers. For a while it was pink and green; one might call the final color "Coral." The adult, which emerged May 3, had normal coloration. (There's no picture because I had to open the container it was in to photograph it, and it flew away before I could focus the camera....)

The experiment demonstrates that a Gray Hairstreak caterpillar can indeed become pink. Dan Hardy's photo, which can be seen here, shows the similarity of the Mexico caterpillar to the one I raised.

To see a life history of a normal Gray Hairstreak caterpillar, click here.

Since the above was written, I found a Gray Hairstreak caterpillar on the Coral Vine at my house, which demonstrates they will use the vine naturally. Rather than feeding on fresh flowers, this caterpillar was feeding on the pale leaf-like appendages that cover the forming seeds. As a result, it was an off-white color, as can be seen in the picture below.

Gray Hairstreak caterpillar on Coral Vine, 5-6-09, Falcon Heights, TX.