This year is proving to be a good one in New Hampshire, if a slightly puzzling one, for the most iconic of all butterfly species – and sorry, Karner blue, but we mean the monarch butterfly.

“It’s been a fantastic year for monarchs. People keep bringing containers of them from their yard, looking for more milkweed to feed them. We’re overrun,” said Sam Jaffee, founder of the Caterpillar Lab, an educational and research site in Marlborough. “It’s a good year in general for migratory species.”

“This really seems to be a bumper year for them,” said Don Chandler, an entomologist at UNH, who lives in Dover. “I’ve never seen so many caterpillars at least in the last 10 years. … In contrast to previous years, where I could see maybe two adults during the summer in Dover, it has been an outstanding increase.”

Chandler said it’s not just the number of butterflies and caterpillars he has seen, but when he has seen them.

“I actually saw monarch caterpillars on milkweed in July, which I had never really seen before,” said Chandler. “The season has been unusual, in that it was cold and wet early, then a decently hot mid-summer, so we saw the monarchs at a time when they should have been migrating north to Canada, not really laying their eggs and producing caterpillars here. So that was a surprise.”

The black-and-yellow monarch butterfly has a complicated, multi-generation life cycle that makes it vulnerable to a host of problems. Eastern monarch butterflies overwinter in the mountains of central Mexico. They travel up to the  Northeastern U.S. and Canada, eating milkweed plants, their only source of food, but it can take them two or three generations to get here, and they spend another generation in this region before they head south to Mexico for the winter, finding a location that was last seen by their great- or even great-great-grandparents.

This unusual pattern means that bad weather or destruction of habitat in a multitude of locations can disrupt the population.

In recent years New Hampshire has seen relatively few of the large, fat monarch caterpillars with their yellow, black and white stripes or the iconic butterflies, amid concern of a population crash of the Eastern monarch. (The Western monarch, a distinct population which flies between Mexico and California, has been more stable. )

This year’s butterfly boom might reassure some, but it’s too early to be sure.

“When it comes to insects, you have to look at many years. This hasn’t established a trend,” Chandler cautioned. “You can toss out all sorts of suppositions and hypotheses, but they have to be tested.”

Jaffee agreed.

“The big crash was largely blamed on weather events during migration. We’ve been waiting to see whether or not they were able to rebound like they have in the past,” he said. “Right now, monarchs are thriving right here in New England, but a few bad weather events and the population could be down again. Then the question would be are there enough pollination sites and native habitat left to start building them up again.”

Interest in monarch butterflies comes amid concern that insect populations in general are declining for a wide variety of environmental and climate-related reasons.

“Perhaps it is premature to talk about monarchs’ risk of disappearing, but the attention they’ve brought to the whole issue of insect decline is valuable,” he said.

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