Crocus Geometer Caterpillar and Adult

2021 January 24

Right at the moment, I am working through a set of photos that I took about a year and a half ago, and I’ve kind of forgotten some details that I really should have written down at the time. Like this inchworm. The date is from June 25, 2019.


The plant it is on looks like Rosemary, so I think what happened here is that Sandy was out collecting some herbs for cooking and found this caterpillar in her herb garden.


It does a pretty good job of imitating the needle-like rosemary leaves, with its legs tucked in close to make its head look like a bud.


And, of course, its rear has two pairs of legs to grab on, and they are shaped so that they look like the base of a leaf.


Once it was done pretending to be a leaf, it spread its legs out so they could grab on to things.




And once the legs were ready to grab, it could then proceed to inch along at a brisk clip, like it was doing here on my finger.



OK, so this was clearly an inchworm, which makes it a “geometer” moth. Since it was a green one, I was thinking that it might be tricky to identify, and I got to wondering why I didn’t try to rear it to adulthood (which would have made it a lot easier to ID). Oh well. So, I sat down with “Caterpillars of Eastern North America” and started browsing. And I found a few candidates, including the Crocus Geometer.

. . . and then I looked ahead at the rest of the set of photos this came from, and saw that I had pictures of a Crocus Geometer adult . . .

Say, what were the dates on these? Hm, it looks like they are about two weeks apart. That’s usually about how long it takes a moth to pupate.

Oh, and look here – there is a picture of a pupa, with a date about halfway between the caterpillar and the moth . . .


And that’s about the point that it all came back to me. I had reared that caterpillar to adulthood to make it easier to identify, and it was a Crocus Geometer caterpillar! And I had forgotten all about it.

So anyway, here is what emerged from the pupa on July 12, 2019:





Crocus geometers (Xanthotype sospeta) are apparently pretty common around here, since this is at least the third time I’ve photographed one (most recently on July 24, 2016, and before that on June 29, 2015). There are actually a couple of other moths in the same genus that look really similar, so it is possible that I am off on the exact species, but we’ll keep going with “Crocus geometer” for now.

Anyway, I had thought it was really unusual for the caterpillar to have been eating rosemary. Basically nothing eats rosemary, in fact its chemical defenses against being eaten are exactly what makes it useful to humans as a spice. At first I thought it was another case of a parasitized caterpillar eating a somewhat toxic plant in an effort to kill off its parasites, but the fact that it matured without mishap kind of shows this not to be the case. Reading more about Crocus Geometers, I find that they are mostly kind of vague on their foodplants. They are apparently generalist feeders on a lot of different things. Interestingly, some of the plants listed are also pretty strongly chemically defended, including dogwood, willow, catnip, and goldenrod. So, it looks like we can add rosemary to this list.

It is kind of interesting that nobody seems to list crocuses as a foodplant, though. Not what you would expect from the moth’s common name, is it?

One Response
  1. January 29, 2021

    Gorgeous as usual!

    When I saw the first photo, I thought you were writing a post on green beans.

    What a great name – a Geometer. That made me smile. Hurrah for math smirking!

    It became a very handsome moth. Your photography did it justice.

    We have rosemary here and it didn’t occur to me how hardy it might be because of its fragrant oils. Most illuminating.

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