Fall armyworms are more like “summer” armyworms this year due to unseasonable rains, according to a Texas A&M AgriLife Extension Service entomologist.

“It’s related to the rains we’ve had in July,” said Dr. Allen Knutson, AgriLife Extension entomologist, Dallas. “The rains were favorable for crops, but they also set up conditions for armyworms to survive and increase in numbers.”

The armyworm is named for its habit of moving across pastures in large numbers like the legions of an advancing army, devouring grasses in their wake, Knutson said. Fall armyworms are called “fall” armyworms because in a typical year that’s when they usually make their appearance in greater numbers.

But this hasn’t been a typical year, he said. July through early August is usually the hotter, drier period in much of Texas, he said. This year, more rain – sometimes in quite heavy amounts – came in late June and early July.

This unseasonable rain is what’s behind the early arrival in large numbers of fall armyworms, Knutson said.

 “It’s an interesting situation,” he said. “Armyworms cannot overwinter in the northern parts of Texas. It’s too cold for them. They all die off in the first cold weather in November. But they continue to survive in the upper Gulf Coast.”

Armyworms are the larval form of a migrating moth. In the spring, the moths begin migrating northward from the Gulf Coast, looking for favorable places to lay eggs.

 The eggs hatch within about four to five days, “regardless of weather conditions,” but few of the young larvae survive when it’s hot and dry, he said. Each female moth can lay as many as a thousand eggs. This year, the larvae found favorable conditions thanks to a wetter-than-normal mid-summer, Knutson said.

Also there are indications that the migrating moth populations are higher this year, he said.