Another Twig Mimic Inchworm

2012 April 25

Sam found this lichen-covered rock with an inchworm on in on June 6, 2010. I’m pretty sure that the inchworm wasn’t eating the lichen, because the camouflage is all wrong.

It’s disguised as a twig, and the way it is posing, it would look pretty darned convincing if it were on a tree. But, being on a rock with a blue-gray lichen, it stands out like a sore thumb.

This is clearly an inchworm, in the family Geometridae. The lack of all but the last four prolegs is pretty distinctive of that family. Unfortunately, a very large proportion of inchworms are stick mimics, which means that they all look a lot like sticks (and, therefore, closely resemble each other). I’m finding a lot of geometrid caterpillars that look pretty similar, but none that I personally feel I can unambiguously say, “Yes, this is the one!” The folks on BugGuide had to think it over for a while, but the eventual consensus was the Porcelain Gray, Protoboarmia porcelaria).

I really should have raised it to adulthood to identify it with certainty, but unfortunately we didn’t have any idea about its foodplant. It kind of looked like it was trying to eat the lichen, but somehow I don’t think that was what it should have been eating. Although, it was pretty big, so it may have been just looking for a good pupation spot.

When it was trying to hide, it tucked its head in and pulled in its legs so that its head would look like the bud scar at the end of a twig. Pretty convincing, overall.

One Response
  1. April 28, 2012

    I’d love to have seen the full-res version of this one. The tiny geometry of the lichen and the contrast of the inchworm make for a beautiful picture.

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