Light Green Caterpillar with Black Spots

2014 October 29

Sam found these two light-green caterpillars with black spots on September 8, 2013. They were inside of a Queen-Anne’s-Lace seedhead [1]

The smaller one sure looks like the same species as the larger one, but one or two molts younger

The size of the spots is fairly unusual, most green caterpillars only have tiny spots.

There is a black collar, but the head is not a uniform black.

They don’t appear to be noctuids at all, so my primary reference book (“Owlet Caterpillars of Eastern North America) wasn’t too helpful other than for telling me what it wasn’t. I actually found one possibility myself on BugGuide: the Parsnip Webworm Moth, Depressaria pastinacella. Only one problem: the page is very emphatic about the caterpillars only eating parsnips. And while parsnips and carrots are related (to the point that historians are often not sure whether literature from the Roman era is referring to one or the other), they are not the same thing. Also, it has more black on the head than the caterpillars we found.

If we go up to the genus level, there is a closely-related moth – the Purple Carrot-Seed Moth, Depressaria depressana. While there is no picture of the larva on BugGuide, the description does specify that “The larvae feed on plants in the parsley family, mainly the flowers and unripe seeds”. And carrots, feral or otherwise, are in the parsley family. However, when I specifically look for the D. depressana caterpillar, the only picture I find is this one. Which shows a green caterpillar with white spots! So, this is looking unpromising.

But! On the other hand! It may be something completely different! I posted these on BugGuide, and John and Jane Balaban gave me yet another possibility – the Carrot Seed Moth, Sitochroa palealis, which is one of the Snout moths, and is in a completely different superfamily! This species looks like a pretty much perfect match in all respects, so I’ll go with it.

The funny thing is, all three of my candidates are invasive species from Europe, mostly of fairly recent vintage (two came over in the last couple of decades). I guess this makes sense, considering that their preferred host plant is also an invasive European species.

At any rate, we have a lot of them around these days. I’ve found several of them myself in the last few weeks, by looking for tightly-curled Queen-Anne’s-Lace seedheads and prying them open. I usually find one or two of these caterpillars in there. It is a bit weird that when I find two, so far there has always been a big one and a small one, and not two of the same size. We certainly have a lot of their food plant around, so there will probably be a population explosion over the next few years.

[1] These are basically feral carrots. They’re everywhere around here. Along with other invasives like spotted knapweed and tansy, they make up the bulk of our fall-blooming flowers.

[2] The Parsnip Webworm and Purple Carrot-Seed Moth are both members of the Superfamily Gelechioidea, which is considered to be at the same time one of the largest, and one of the least well described, of all of the moth groups. They tend to be “micromoths” that are hard to find, hard to distinguish from each other even when found, and very widespread. There are about 16,250 named species in the superfamily, and rough estimates are that the named species only make up about 25% of the total species.

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