Invasion of the Millers


WYOBRASKA – It seems that every time a door is opened, miller moths take to the sky. There is even a chance to get these insects with your mail. 

And, while the moth is nothing new for the area, the numbers have been higher than in previous years. 

Miller moths or millers for short are the adult stage of cutworms. Jeff Bradshaw, Entomology Specialist/Interim Director at the Panhandle Research and Extension Center in Scottsbluff, Neb. said, “The time period around late May to June is when you typically see those adult moths flying about.”

The millers migrate every year following the flowering plants which are energy sources for the insects. “The adult feeds on flowers so it’s looking for nectar,” said Bradshaw. “That moth is going after whatever is flowering.”

Scott Schell, Entomology Specialist at the University of Wyoming Extension said, “The flowers that they visit are the ones that stay open at night because being moths that’s their preferred activity time.”

The number of miller moths each year depends on many factors. Whitney Cranshaw, Entomologist at the Colorado State Extension, narrowed it down to two main factors. 

“As always the potential for nuisance problems with miller moths is largely based on two factors. One is the numbers of the insect that develop in the spring of the year,” said Cranshaw. “The second factor that influences the severity of nuisance problems with the moths is the abundance of flowering plants.”

Cranshaw explained this year is different than previous years due to lower moisture conditions and less blooming flowers along with a spring freeze.

“Army cutworms are pretty interesting. They’re unique in how they migrate,” said Bradshaw. “These move from east to west. What they’re actually doing is moving up in elevation or down in elevation depending on the time of year.”

Millers will make this trip twice if they survive the summer. Bradshaw said that moths “are actually a really important source of protein for bears through the summer.”

The insects will lay their eggs when they return to the plains in the fall. “They prefer to lay their eggs in sort of bare patches or less vegetatively dense patches so newly planted wheat fields or newly seeded alfalfa,” said Bradshaw.

While the moths are not particularly dangerous to crops themselves, their larva and caterpillar stage are. 

“Cutworms are called cutworms because they cut the plant so actually the plant at the base,” said Bradshaw.

 Schell said, “If you’re out in the garden or something like that, you flip over a piece of landscaping or you do a little digging and one of those caterpillars comes up and they form this immediate ‘C’ shape.”

Cutworms are most commonly found in wheat and alfalfa fields in the spring. These insects can cause the loss of an entire crop if left unchecked.

“In really bad outbreak years, you can have areas of rangeland that are visible. If you fly over them, you can see bare patches that are due to cutworm cutting,” said Bradshaw.

One of the most common miller moths that is found in WyoBraska is the army cutworm. These insects spend the winter in the soil and are one of the first to be seen come spring. “The army cutworm is probably our most abundant and that’s probably because they’ve adapted to feeding on small grain crops,” said Schell.

According to an article from the University of Nebraska-Lincoln’s Cropwatch, “In infested fields, you may see higher than usual bird activity, especially in the early morning; birds will often feed on army cutworm larvae when they are in high numbers.”

Scouting for these caterpillars is encouraged and insecticides should be considered for high concentrations of cutworms. Bradshaw said, “We usually look at controlling cutworm damage in kind of an April-May time period when the larvae are active in the soil.”

Producers should also look out for other types of cutworms. “We have some other cutworms that occur at other times of the year like the western bean cutworm which is a different kind of cutworm that is important in dry beans and corn,” said Bradshaw.

Millers can be controlled using a light trap. In the home, simply placing soapy water near a light source will help control the insect.

The miller moths time in the area while very brief is dependent on temperature. “The length of time the moth migration will continue depends largely on temperature. Flight activity of this moth will accelerate with periods of warm nighttime temperatures,” said Cranshaw.

Bradshaw said the number of millers this year was a moderate total compared 2019. 

Cranshaw said, “The numbers of miller moths in late spring is primarily related to the numbers of army cutworm caterpillars which occurred earlier in the season. Outbreaks of the army cutworm are usually followed by large flights of miller moths.”

More information on cutworms or miller moths can be found by contacting your local extension office.

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