We've been getting questions (most of them tinged with relief) about why miller moth numbers seem so low this year.
Whitney Cranshaw — a Colorado State University extension specialist in entomology who we turned to in our fight against yellow jackets — said that the number of miller moths this year was the lowest he's seen since he moved here in 1983.
"They were almost a complete no-show this year," he said.
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"Miller moth" is the commonly used name for the army cutworm, a caterpillar that often damages young plants. Sometimes, large numbers of the crawlers travel in army-like groups, which is where they get their name. In the spring, they burrow into soil and emerge three to six weeks later as moths. The adult insects fly from the middle of May through the month of June, so there's no surprise they're not out now. Their minimal presence earlier this summer could be due to any number of factors, Cranshaw said.
There's no way to know exactly what contributed to the decline, but insect populations are largely influenced by their environment. When the factors that control them align, they suffer a low-number year. In the average year, only two of 100 army cutworm eggs make it to adulthood. In a good year, five of 100 might make it. This year, Cranshaw said, perhaps less than 1 in 100 survived.
"It's tough being a bug," he said. "It may look like they're doing great because there are a lot of them, but they have high infant mortality rates and lots of things hunting them."
Army cutworms fall prey to parasites, predators and the weather. As caterpillars, they're hunted by crown beetles, parasitic wasps and birds. Bears overturn the rocks that they hide under and gobble them up. As moths, they're also hunted by birds and bats. In some years, a "perfect storm" of factors will suppress their numbers, Cranshaw said.
Despite this year's low turnout, though, the critters are not eliminated and might very well have a strong showing next year.
For those who hope for a repeat of this year, Cranshaw provided a few tips. Those include cutting down weeds and dense vegetation in late August and early September so cutworms don't have a place to lay their eggs, as well as rototilling in early spring to kill young cutworms.