Large Black Moth – Ctenucha virginica

2007 September 9

These large moths were pretty plentiful back in June (as in, I saw about a dozen of them this year). This particular one was attracted by the light from our back door at the time. The blue on their body is actually very iridescent (an effect that I have a hard time capturing on camera).

ctenuchavirginica.jpg

This is a Ctenucha virginica, a type of large “wasp moth”. For size reference, it is resting on a playing card [1]. There are a couple of things about the name that are a problem. First, how the heck are you supposed to pronounce “Ctenucha”?[2] Second, the name “virginica” leads one to believe that they are a southern species, with Virginia being somewhere in the middle of their range. This is a lie. It turns out that they are a northern species, common in the northern US and Canada (and here, of course), and Virginia is the extreme southern portion of their range.

ctenuchavirginicaface.jpg

There is a similar species, the “Yellow-Collared Scape Moth[3]” (Cisseps fulvicollis) that can be mistaken for this one, except that Cisseps fulvicollis has a larger orange patch that runs straight across the thorax, while Ctenucha virginica has a smaller orange patch that kind of “drapes around the shoulders”

ctenuchavirginicaheadantennadetail.jpg

Based on the size of the antennae, I expect that this one is a male (since male moths tend to have larger, featherier antennae so that they can track down the scent of the females). I’ve seen them flying around in broad daylight, and this one was drawn to a light during the night, so they evidently don’t much care about what time of day they are out hunting for food (the adults drink nectar from flowers). They are pretty strikingly visible during the day, so they must have some defense against getting eaten, but I don’t know what it is[4].

Anyway, according to BugGuide, the larvae “feed on monocots: grasses, sedges, iris”, which seems to me to be a weird list. Why iris? And will they eat any grass (keeping in mind that things like corn can be considered grasses), or just the sorts of species that people use for lawns?

Edit: Much later, I found and photographed the caterpillar, which I posted about here. The caterpillar is pretty distinctive, too.

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[1] I mainly used the card because it was hard to get good contrast of a black moth against any sort of dark background. It was the Ace of Diamonds from a “bicycle” deck, if anyone wants to get the scale by measuring the visible diamond symbol. It was big enough that I couldn’t easily use the high-magnification “macro” lens, because it wouldn’t all fit into the picture.

[2] If this were in Esperanto, then I would pronounce the “C” as if it were a “Ts” sound, but it isn’t in Esperanto. So, I don’t know if it is pronounced “ts”, “k”, “s”, “ch”, or, for all I know, “xyzzy”

[3] Whoever came up with the common name for this evidently had the same color naming convention as my father. We had one of those orange “outdoor” extension cords, that he consistently referred to as the “yellow extension cord”. And now, when somebody calls something “yellow” that is clearly orange, I don’t even register that they called it the wrong color.

[4] One possibility, given that they are referred to as a type of “wasp moth”, is that they look enough like a wasp that predators don’t want to tangle with them. I kind of doubt this, though, because they don’t look *that* much like a wasp.

11 Responses leave one →
  1. June 19, 2009

    I found out when poking around that “virginica” is a tip of the hat to Queen Elizabeth I – the Virgin Queen. Just thought I’d share that random tidbit with you!

  2. Carol Liller permalink
    July 6, 2009

    Hi!! I have about forty of these circling my backyard, making me very nervous. I was able to look at one close up (the yellow-collared scape moth) which did nothing make me feel better :=) However, I decided that if they were pretty orange coloured butterflies, I’d think nothing of having them flit from my bushes to my trees and decided to just enjoy them. I’d never notised them before, but this is the first year I have put bird feeders in my orange tree and I have a fine crop of dracena, or corn plants, growing as well as other grasses and flowers-so your theory about what ‘grasses’ they are attracted to is right. The birds leave them alone, probably because they do resemble wasps. They also stick around all day and cluster between the rubber tree, a large ‘Snow on the Mountain’ and the orange tree. Thanks for your page-I’ve found it invaluable when looking for the flying and crawling beasties in my little world.

  3. July 6, 2009

    Thanks for the added observations! We actually have quite a number of them this year too – I’ve seen about a dozen of them so far in the last week. It must be a good year for them.

  4. Lee permalink
    June 12, 2010

    We have what seems like hundreds of these around our yard. They are plastered all over our bushes, and flying everywhere, landing on the windows, day and night. Never noticed them before this year. I don’t like them, they seem to chase me when I’m outside. I’m very imtimitated by them, does anyone know if their harmless? Do they sting? Can I use a spray to kill them?

  5. June 13, 2010

    They are completely harmless (moths don’t have stingers, and they don’t bite), although I agree that these jet-black things can look a bit sinister. They’re only going to be around for a couple of weeks before they die off, so there’s no real need to do anything about them. The larvae eat grass, so they aren’t likely to damage any of your garden or ornamental plants, either.

    The way these things usually go, the large numbers this year will cause a big increase in the number of their predators and parasitoids. This means that next year, there will be so many things eating the caterpillars that they are likely to be almost wiped out, even without you doing anything.

  6. June 13, 2010

    I have them in my storage shed that is attached to my patio of my condo. There were 2 of them today and one flew into the condo. They look creepy. I sure don’t want them sitting on all my things stored in the shed. Larger pots and pans, baking items etc.

  7. Ed Hayden permalink
    August 11, 2011

    Saw a dozen of these Virginia Ctenucha flitting about a meadow by the seashore in Bellevue, Newfoundland, today. Simply stunning. Thanks for the very helpful information you’ve posted.
    Ed Hayden

  8. joann permalink
    July 12, 2012

    Thank you for the information. I just had one fly into my house in Nova Scotia. I have never seen a black moth before.

  9. Matt permalink
    July 14, 2012

    Awesome! I’ve been looking for the name of this moth! I live in Petaluma, California and have been seeing these around the property I live on. Any idea on why they might have spread this far west or is there a western species that I’m confusing it with?

  10. July 16, 2012

    Matt: I’ve been seeing a lot more of these than usual lately, too. About a month ago, over a dozen of them came to our porch light. Since they eat grass, it is quite possible that they are living in some quantity in people’s lawns, and it would not surprise me at all if they were expanding their range cross-country by lawn-hopping.

    They could also be the very similar Yellow-Collared Scape Moth, which is known to live in California. Check it out here:

    http://bugguide.net/node/view/447

  11. Matt permalink
    July 17, 2012

    Awesome, cool! That’s interesting about the lawn hopping too as I live in the country away from any manicured lawns. Is that just an explanation for their increased range then?

    Also, thanks for pointing out the similarity with the scape moth. I looked at those too, but wasn’t convinced that what I saw was indeed the scape moth as the wings look more akin to the Ctenucha virginica (is there a common name?). Is that just the way they fold or are the wings for the scape moth less broad?

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