Large Yellow Underwing (Noctua pronuba)

June 20, 2002

For this moth, I've reproduced the sidebar from my upcoming book, "Discovering Moths" (Downeast Books, Fall '02).

A New Moth in North America

On June 13, 1996, while black-lighting for moths in my yard, I came across a moth that was not found in any of my field guides. This surprised me since this moth had some notable features that would usually lend a species to inclusion in any the books that were out there.  The forewings of this moth were a dull brown/gray and had black dashes near the tips.  Although at first glance it was a relatively drab-colored insect, its hind wings turned out to be deep yellow with a single black subterminal band, suggesting a Catocala (underwing) moth. The moths in genus are fairly cryptic in appearance when their wings are folded, but can have bright orange, yellow, or red as the base color for the hind wings.  But two characteristics ruled out that genus for the moth I found on that evening.

First, the shape was wrong.  When at rest, this moth had a long rectangular contour, unlike the triangular shape of most Catocalas.  The second, was the single black band on the underwing.  Almost all of the Catocalas with a yellowish base on the underwing have two, or one and a half bands.  None that I knew of had just one.  I was beginning to get excited.  Maybe I had a new record for this moth.  I took a couple of pictures, and figured that at some point I would show the slides to one of the several entomologists in the area.

A week passed.  I was sitting down, casually leafing through a copy of "Butterflies and Moths" by David Carter.  This is one of those Eyewitness Books with lots of great photos of lepidoptera from around the world.  As luck would have it, right there on page 253 was my moth!  It's a noctuid called Noctua pronuba, or Large Yellow Underwing.  Its listed range - Europe, ranging from North Africa to Western Asia!  What was it doing here? And were there any other records?

I sent a message with a description of the moth to Larry Gall, an entomologist with the Peabody Museum in New Haven, CT.  He told me that he had seen the same species for the first time last fall and had found several more on his porch that summer.  He said one was even found flying around inside the car of a friend.  According to his best recollection, this species was relatively new to our state and he suggested I contact David Wagner at University of Connecticut, Anthony Thomas with the Canadian Forest Service and/or Donald Lafontaine form Agriculture Canada.  Larry believed that this moth was first introduced in Canada.

As it turned out, he was correct, and after corresponding with these three people, I was able to gather some more information on this new moth.

I learned that Noctua pronuba was accidentally introduced into Nova Scotia in about 1979.  It was first recorded in Halifax.  It was probably not around much before that, since one was collected in 1979 and it was common within a few years.  In other words if it was there, they would have known it.  It reached Fredericton, New Brunswick and Newfoundland in 1984 and Maine in 1985.  By 1996, it was in Maryland.  Its spread had been well-documented and a number of papers had been published reporting an ever-increasing area of occurrence.

In the UK, this is a very common, sometimes abundant moth.  In recent years I have heard reports of moth collectors being deluged by many hundreds of them at their lights. Given its great bounty "across the pond", one has to wonder what took them so long to get here?

In Connecticut, they were first recorded in 1993 by John Trouern-Trend.  They had been seen in good numbers by several people in my state since then.  Rats, I missed it by three years!  In the big scheme of things, though, that's not very long.

I got a call from a friend that June following my discovery of this moth.  He had found a pupa in his yard and didn't know what they would turn into. When I saw him a week later, he told me that it had emerged and added, ."...and I can't find it in any of the books.."  He then described the Noctua pronubas, which I just happened to have with me.  (I had included some live specimens for a moth exhibit we were running at the New Canaan Nature Center.)

Since then, this moth has become very common in my area.  They appear in my yard from June through September, flying into the lights like drunken bombers.  You actually hear them crashing into the sheet!  It's not uncommon to find a pair mating right on the light sheet.  The females can lay up to four hundred and fifty eggs at a time and the caterpillars will sometimes hibernate through winter, not pupating until the following spring.

Noctua pronuba feed on dock, dandelion, and a variety of grasses.  According to Carter's book, this moth is considered a mild pest of garden flowers and vegetables in Europe.  Given its rapid spread, I wonder if we will be regretting the arrival of this newcomer.  I can't help but wonder if I was among the first to view the moth equivalent of European Starlings, or Purple Loosestrife.  It is not a given that their feeding habits will cause them to fall in such disfavor, but they are worth keeping an eye on.

A few years after finding this moth, I did a cover illustration for The Lepidoptera Journal, a scientific publication put out by The Lepidopterists' Society.  For months after its appearance, I heard from people grateful that I had solved a mystery for them.  They too had come across this moth and could not find it in any of their reference guides.  Like me, they could not understand how such a bold moth - both in appearance and attitude - could have been skipped over in books covering their area.  There is nothing more satisfying than a mystery solved.

For now, I still enjoy seeing those big clumsy moths coming to my lights. They are an attractive insect. I just hope they behave themselves.