Farmers and ranchers in parts of the United States say they're suffering the worst grasshopper infestation in decades. Millions of grasshoppers are eating their way through cattle grazing lands in Midwest and Western states.

According to Dave Stenberg at the University of Nebraska's Agricultural Extension office in Lexington, there are so many grasshoppers in the fields this year, the ground looks like it is moving.

"Many of our pastures were devoured by these insects," he says. "Not only did they eat off the top of the plant, but they ate right down into the crown and into the roots, so some of that grass is gone."

He says grasshoppers are almost always somewhat of a problem by mid-summer, but this year has been the worst all but the oldest farmers can remember.

Extension educator Jason Larson in Broken Bow, Nebraska, stresses a drought and a mild winter has helped create a bumper crop of the insects this year. "And a lot of grasshoppers lived through the winter," he says. "Some producers said they saw grasshoppers around in February, which is very abnormal."

Most years, it is not unusual to see three to five grasshoppers per square meter of grassland. This year, officials are counting 50 or more per square meter. The trouble extends to other states, like Nevada, Utah, and Colorado, where some ranchers reported 200 grasshoppers per square meter. These insects can devour half their body weight in vegetation every day.

No one has added up the economic damage from the infestation yet. According to Mr. Stenberg, cattle ranchers are being hit the hardest. "The cattle in a lot of cases have been moved off the pastures," he says. "They are selling cows, weaning calves at 60 days instead of the normal four-to-five months, and selling the mothers because there is just no feed."

Ranchers will try to keep younger cattle alive using other, more expensive feed, in hopes that the grazing lands will make a comeback next year.

"The concern we have is what are these pastures going to be like in another year? Let's say we go back to normal rainfall," Mr. Stenberg says. "If the grass plant is gone, how long will it take for other plants to fill in that space? Will we have a lot of weeds fill in that space?"

Farmers can spray insecticide to control the grasshoppers, but it can be expensive and government assistance does not cover spraying. Officials say the problem could become worse in the coming weeks, as more of the grasshoppers reach adulthood and have bigger appetites.