Moth Reared from Insect Eggs Found On House Siding – Variegated Cutworm/Pearly Underwing
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.
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.
 Herbivores are sometimes not as strict about their diet as we are commonly lead to believe. Like the infamous chicken-eating cow, for example.