N.M. ranchers fight range worms invasion

/ Source: The Associated Press

It has all the makings of a potential rangeland disaster — thousands of acres of green grass, herds of cattle, antelope and other animals that need to eat versus an emerging army of spiky caterpillars with voracious appetites.

But ranchers are hopeful their quick action will take care of the caterpillars — also known as range worms — before they can wreak havoc on pastures in northeastern New Mexico.

Some ranchers have embarked on a campaign to keep the caterpillars at bay on their property with crop-dusters, pickup trucks outfitted with foggers and an insecticide called permethrin.

They've already sprayed 108,000 acres and have at least 40,000 acres more to go, Union County extension agent David Graham said Tuesday.

"We're trying to knock them back," he said as he prepared for another day of spraying.

While ranchers in northeastern New Mexico regularly live with range caterpillars, Graham classified the latest invasion as "the worst case we've had in 10 years."

Like anything in nature, caterpillars have a cycle and this summer appears to be one of their peaks. Entomologists say recent moisture and the resulting green pastures could help this year's caterpillar population, but ranchers' efforts and natural predators could keep them in check.

"They're boom and bust insects," said David Richman, a science specialist at New Mexico State University in Las Cruces. "They come up and they go down. They come up and they go down. It's hard to predict."

Always hungry
One problem is the caterpillars' appetite. Graham said research has shown that just a few of them can eat as much grass as a yearling cow.

Don Schutz, a rancher in the Wagon Mound area, has witnessed the caterpillars' technique.

"It's just this mass of moving worms" when the population becomes overwhelming, "and they form these windrows and you can have a foot of green grass in front and desert behind it," he said.

The other problem is that the caterpillars, which can grow to a couple of inches long, are lined with tiny hairs shaped like tree branches that sting.

Ranchers say that's not good when you have yearling cattle that are eager to put their noses in the grass and start chomping.

Graham said it also can be painful to handle the yellow caterpillars or kneel in infested grass.

The heaviest infestation, Graham said, is along the west end of Colfax County and part of Mora County north of Las Vegas. There also have been reports of caterpillars in Union and San Miguel counties.

Ranchers are paying about $1.25 per acre to spray for the caterpillars. Schutz has sprayed about 4,000 acres but said others have sprayed as many as 20,000 acres.

That's important, according to the veteran rancher, because unless all infested pastures are sprayed, the insects that survive in untreated areas could find their way back to treated pastures.

Schutz acknowledged spraying doesn't always kill all of the pests, but said it at least makes the situation manageable.

Those caterpillars that make it to the pupa stage still have to deal with natural predators like skunks and shrews, Richman said. Beetles, wasps and other parasites also can have an impact during other life cycles, he said.

Graham estimated the spraying would be finished before the weekend, but he added that more ranchers are checking their pastures.

"I had three ranchers come in today," Graham said Tuesday.