For the second year, the kids at Debbie Thompson’s preschool studied monarch butterflies for weeks before bidding them farewell as they took flight for Mexico.

“They are sad to see them go,” Thompson said.

The kids learned about the metamorphosis of the monarchs, from caterpillars to butterflies.

Caterpillars were collected in local fields and brought back to Thompson’s in-home daycare. Placed in a fish tank, the caterpillars formed a dark, green chrysalis before emerging as butterflies after a month.

The butterflies were then transferred to a homemade mesh enclosure.

Before the release on Thursday, Thompson and the kids placed tracking stickers on the underside of the butterflies’ wings. The stickers, which Thompson got from the Lloyd Center for the Environment in Dartmouth, allow scientists and butterfly watchers on the migration route to track the insects.

“We’re helping the butterfly population by doing this,” she explained to the kids.

Outside, the Thompson and the kids released the butterflies one by one, chanting “Gotta go, gotta go to Mexico,” for encouragement.

Thompson said getting the kids outside and learning is a big part of the daycare year round.

“It’s like nature’s classroom,” she said. “We’re looking for moths and birds. For me it’s really cool when we’re out and the kids can identify a cardinal or a woodpecker.”