Moth Reared from Insect Eggs Found On House Siding – Variegated Cutworm/Pearly Underwing

2010 July 31

Back in early May, we noticed a number of clusters of insect eggs that had been laid on the eaves and siding of our house.

They had hatched within a couple of weeks after they were laid, producing dozens of tiny little caterpillars.

These were very similar to some that we found and posted way back in 2007, but that we were never able to identify. And the reason we couldn’t identify them last time, was that we didn’t raise them to adulthood. So this time, we decided to try rearing them. I used a piece of paper to scrape gently underneath the caterpillars while holding a jar below, and collected a huge bunch of them. I figured that, since the mother moth hadn’t made any effort at all to lay the eggs near an appropriate food plant, the caterpillars would probably either be willing to eat almost anything, or their preferred food plant would be something really common in lawns. So, I put a selection of plant leaves (grass, plantain, clover, and dandelion shoots) into the container, and checked to see what it was they liked. It turned out they liked the clover.

They kind of skeletonized the clover leaves at first, stripping out the parts of the leaves between the veins. This was probably because they weren’t big enough to eat the veins yet. At first, they crawled by “inching” along like an inchworm, so I thought that they were some type of geometrid moth.

But, as they got bigger, they stopped inching and crawled like a regular caterpillar. They grew pretty fast, and mostly seemed to go into a torpor during the day, but with a bit of a feeding frenzy at night – I’d top off their cage with clover in the evening, and in the morning it would be gone.

One thing that I noticed was that, while we started with probably 50 or so of the tiny caterpillars, over time there got to be fewer and fewer of them. And yet, during enclosure cleanings, we never found any corpses. Suggestive, isn’t it? Apparently, many kinds of caterpillars will turn cannibalistic if they are too crowded and/or run short of plants to eat. While I never actually caught one of them eating another, I very strongly suspect that this was in fact exactly what was happening[1].

Anyway, after they got pretty big, fat, and sausage-like,

they finally pupated, producing these classic, brown pupae.

They tended to bury themselves under any debris that was at the bottom of the jar they were in, so in the wild they would probably have buried themselves in the soil, or at least under the leaf litter.

And then, finally, after about two weeks as pupae, they started emerging as these gray moths. The moths actually looked rather startlingly like dead clover leaves, making it hard to tell they were there until I poked the “leaves” with my finger and some of them flew away.

On BugGuide, John Schneider thinks they are probably Pearly Underwings, Peridroma saucia, which as caterpillars are often known as Variegated Cutworms. They are very widespread, found throughout North America and most of Europe and Asia. Like other cutworms, the are pretty wide-ranging in their tastes, and are major pests of a lot of garden plants. However, they are nocturnal and so usually don’t get caught in the act very much. They are also somewhat atypical of cutworms, in that they don’t chew off plants at the base. Instead, they crawl up into the foliage at night to chew holes in the leaves, then drop back into the soil to hide during the day.

Anyway, a few days after our moths emerged, we noticed another egg deposit on one of the house windows. So, the cycle starts again now. I expect that this second brood will get up to pupating right about autumn, then overwinter as pupae to emerge in the spring.

And, now that I know what they are and how to cultivate them, I could potentially start raising the caterpillars as food for predatory beetles. I understand that, say, Tiger Beetle larvae are particularly fond of this sort of caterpillar.

————-
[1] Herbivores are sometimes not as strict about their diet as we are commonly lead to believe. Like the infamous chicken-eating cow, for example.

16 Responses leave one →
  1. July 31, 2010

    I love it! You’re getting to do things I wish I was doing. :-)

    When they turn cannibal, they must find their littermates’ bodies easy to penetrate and their juices easy to suck. I wonder if eating all that clover gives them a vegetable musk that makes them easier to find by the other caterpillars. Or do you suppose that in the overcrowding, they just stumble upon each other and chow down?

  2. July 31, 2010

    It was pretty crowded in the container (it was one of those 1-lb salad containers that you get from places like grocery-store deli sections), and they were pretty much crawling over the top of each other, so specifically seeking out victims was not necessary. I am curious about whether they actually attacked each other while alive and healthy, or if they only ate the ones that were weak or dying already. I’d probably have to check on them in the middle of the night to find out, during the day they just kind of laid next to each other in a torpor.

    Incidentally, there are a few carnivorous caterpillars. This post talks about a predatory inchworm that actually actively hunts for prey. It’s in Spanish, but Google Translate does a pretty good job on Spanish text. Besides, the picture of the inchworm snatching a fly pretty much speaks for itself.

  3. August 1, 2010

    Tim, what’s the scale on that first picture – how big was that egg cluster?

  4. August 1, 2010

    The eggs were individually about a half-millimeter in diameter. The whole sheet of eggs was probably about an inch across, so there were a lot of eggs in each one.

  5. August 1, 2010

    Wow – very cool. You have eagle eyes to notice something like that!

  6. August 2, 2010

    Well, my family has eagle eyes, at any rate – I think it was Sandy that spotted the first batch. Once we started looking for them, we found probably 20 or so deposits all over the house exterior.

  7. August 3, 2010

    We were at the top of Haleakala two days ago and the wildlife information board talked about a predatory caterpillar that would reach out and grab other insects to devour them.

    As for monitoring the caterpillars at night, I’d suggest a Kodak Zi8 set at the lowest resolution and with a monster memory card. It would be like a security camera at a convenience store!

  8. August 19, 2010

    As much as I like bugs (in general), this pic of the eggs is a little creepy for me. I used to raise caterpillars into butterflies when I was 6 or 7, but never at the eggs part, only from the cocoons I found.

  9. Tabitha Jackson permalink
    August 21, 2010

    I live in Northeast Arkansas and for the last two weeks or so we have woke up every morning to these little catapillars creeping under the backdoor into the kitchen floor. Throughout the day they make there way all around the house. I have found them burrowing into the carpet even. In the last couple days they have been accomponied by little black centipede looking critters with hook like fangs on the front…really creepy. I think they are what you have described, but I’m not sure. We have no house plants but I still find the little egg clusters everywhere; inside and out. We live next to a bean field so is it immpossible for me to get rid of them?

  10. August 22, 2010

    Tabitha:

    It sounds like they are coming in through doors and windows, probably from adult moths coming off of the bean field. Your best bet would most likely be to just scrape off egg clusters near the doors and windows as soon as you find them. Also, if you have any outdoor lights, maybe turn them off to keep from attracting the adult moths to your house. Or set up a light at some distance from your house to attract them to that instead. Other than that, you probably will just have to live with them – there are probably tens of thousands of the adult moths maturing out in that bean field. In any case, they won’t be able to survive in your house without plants to eat. They will either dry out or starve fairly quickly. They aren’t like clothes moths or carpet beetles, which can eat fabric and hair that they find in the house.

    The centipede-like things are probably predators following them in to eat them, so they won’t be a long-term problem either and will most likely go away as soon as the caterpillars do.

  11. Della3 permalink
    August 31, 2010

    The eggs are beautiful! The picture looks like a pearl-encrusted brooch.

  12. Bob Joe permalink
    May 27, 2012

    We found a cocoon just like this. At first we thought it was wood . . . we crushed with a rock not knowing what it was . . . and it splattered white goo all over us! Don’t ever crush something when you don’t know what it is.

  13. JonPbo permalink
    June 14, 2012

    I live in Southern Ontario Canada and seem to be getting these eggs laid on laundry hung out on the line. Was very happy to find an exact match to the eggs we’ve been finding and not something that poses a big threat or nuisance.

  14. mike permalink
    May 17, 2013

    Kill them ASAP!
    Why would you let that nasty creature consume and kill your plant life?

  15. Azriel permalink
    June 17, 2014

    I found a caterpillar in my house lol I still have it but it’s pupated right now I have no idea what kind of moth it is the caterpillar was a strange pink color and had like a orangish underbelly but still it’s really cool

  16. Chris permalink
    July 14, 2014

    I live in Navarre Florida (just east of Pensacola Fl on the Gulf Coast) and found these the other day on my back porch. The egg “sacs” look like smeared peanut butter with clearly dozens of eggs attached to it. I went out tonight to see what was laying them and the grey moths were flying all around and I actually caught a few in the act!! I cannot live with smears of peanut butter looking eggs on my siding so will be investing in a couple bug zappers tomorrow :)

Leave a Reply

Note: You can use basic XHTML in your comments. Your email address will never be published.

Subscribe to this comment feed via RSS