Fewer Than Normal Miller Moths in 2007, Says Colorado State Entomologist

It will be a below-average year for miller moths along the Front Range of Colorado, according to Colorado State University entomologist Whitney Cranshaw. Low numbers of caterpillars and the effects of snow cover from heavy winter storms will reduce encounters with the moths as they make their annual migration to the mountains from the plains.

The army cutworm is the most significant moth-nuisance problem observed during spring in eastern Colorado, sometimes invading homes as it makes annual migrations, said Cranshaw, a professor in the Department of Bioagricultural Sciences and Pest Management at Colorado State. Very few moths were produced in 2006 which created the smallest flight in over two decades.  

"This year there will be a few more moths than last year, although numbers will still be low by historical measure.  However, the moths that are present will be well spread out and not ‘in our face’ during the migration flight," Cranshaw said.

Perhaps the most important factor affecting miller moth problems will be the great increase in native flowering plants this year due to this past winter’s snowfall and rain.  Adults of the army cutworm seek out flowering plants in the course of their annual migration from the plains to the mountains.  

In spring 2006, there were very few flowering plants due to severe drought.  These circumstances concentrated the relatively few miller moths into the relatively few patches of flowering plants – mostly irrigated and landscaped areas around homes.

"There was a strong ‘oasis effect’ in 2006 where most of  the moths along the Front Range spent at least some time near flowering plants in close proximity to humans," Cranshaw said.

In 2007, this situation is very different.  Excellent winter snow cover and good rainfall through essentially all of eastern Colorado will promote huge amounts of wild flowering plants that serve as nectar sources for these insects.  This will spread out the activities of the migrating moths, causing a smaller percentage to remain around flowering landscaped yards.

Flights of miller moths also will be later than average as well.  Due to the snow cover and cooler winter temperatures there was likely little development of the caterpillars during the winter months.  Flights have begun as early as late April in some years but large numbers of moths will not likely be seen until after Memorial Day along the Front Range this year.

For more information on the biology and most questions that involve this species in Colorado please refer to the Colorado State Extension Web site at http://www.ext.colostate.edu/Pubs/insect/tips-millers.html.