Large Yellow Underwing Caterpillar, Green Phase

2021 March 28

Sandy found this fat green caterpillar while preparing the garden for winter on October 25, 2019.


As it happens, this was actually the same species as one that I photographed way back in April of 2007. That one was tentatively identified as the caterpillar of the Large Yellow Underwing, Noctua pronuba. At the time I only got one photograph, which didn’t show much in the way of ID features, so it sure looks like time to give it a go again.

The main ID feature is the color, combined with the markings on the back: two rows of black dashes running the length of the body.


The head is a uniform tan color,


and there are no particular markings on the underside.


An important point is that they aren’t always this color. They apparently hatch out as a light brown color, and then in the fall they turn green like this. After hibernating underground as a green caterpillar, it looks like they then molt one more time to turn a mottled brown color, eat some tender spring growth, and then pupate into these large (a bit over 1″ long) moths, which I photographed back in July of 2016.


They apparently eat pretty much anything as long as it is young and tender, since as cutworms they shear off new seedlings at the base. You do not want these in the garden. One of the benefits of tilling the garden in the spring, is that you turn these up. And if it is early in the spring, just after the snow melts, their lurid green coloration makes them easy to spot. And then when you toss them to the chickens, the chickens will fight over them because they are evidently delicious.

One Response
  1. April 8, 2021

    It’s interesting that they’re not green in the spring and brown in the fall. Oh well. I guess there’s only so much evolution can optimize.

    I wish I had chickens, too. When we groom our raised beds, there are usually a ton of grubs in the soil. It would be great fun to treat the hens to some grub grub.

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