CANTON - Red Admiral butterflies are invading the north country along with other parts of the country and Canada, likely because of a mild winter that created a high survival rate and because of winds that carried many of them northward.

The butterflies, whose Latin name is Vanessa atalanta, pose no threat and are native.

“It’s one of these natural phenomena that people should watch and enjoy,” according to Wayne K. Gall, a regional entomologist with the state Department of Health. “They’re not harmful in any way. This is repeated every year but this year they’re here in greater numbers. They’re moving large numbers across a broad front.”

Reports of similar high numbers of butterflies have cropped up in Ohio, Chicago, western New York and Toronto, among other locations.

The Red Admiral is native to western and central New York and can overwinter as adults. Western New York saw the first major movement of the butterflies April 14 and 15 when their appearance was accompanied by a strong warm front, Mr. Gall said. On Thursday, there was another movement with strong southerly winds pushing them north, he said.

Mr. Gall said this year’s migration is the largest he has ever seen.

Red Admirals prefer a plant in their diet that many people would prefer not to have in their yard.

“We’re probably going to have quite a crop of caterpillars eating the nettles,” Mr. Gall said.

Overwintering survival rates in cold areas are low but migrating butterflies breed and repopulate northern climates.

If the butterflies and their pupae survived the north country’s relatively mild winter, this spring’s population was likely supplemented by travelers from the south, Mary S. Rutley, Colton, a retired SUNY Potsdam biology professor, said.

The Red Admirals are not moths. Butterflies are generally active during the day while moths are primarily nocturnal, Mrs. Rutley said.

Other differences are that moth pupae are found in cocoons while butterfly pupae are in a chrysalis of hardened protein. The antennae of butterflies are delicate with knobs on the ends while moth antennae are more feathery, Mrs. Rutley said.

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