CHICAGO (CBS) — Scientists and volunteers are spending their time putting 2,500 caterpillars to bed for the winter on the roof of the the Peggy Notebaert Nature Museum in the park of Lincoln Park.

As WBBM Newsradio’s John Cody reports, Notebaert Museum biology curator Dr. Douglas Taran says the purpose of the effort is to produce healthy populations of three imperiled butterfly species: the Baltimore Checkerspot, the Regal Fritillary, and the Swamp Metalmark.

LISTEN: WBBM Newsradio’s John Cody reports

Taran turned common household items into habitats that protect the caterpillars from the worst of the winter chill and the drying effects of winter’s low humidity.

He says the butterflies need the cold to progress to their adult phase. But too cold and too dry kills them.

So he pours into a drinking glass, plaster which will retain moisture over the winter. Then butterfly caterpillars are put in the glass, a lid is snapped on, and it is placed under terra cotta flower pots which even out temperature swings.

“A lot of these species eat violets, so we’ll be watching the violet leaves around the museum grounds,” Taran said. “When they start coming up and turning green, we know that it’s time to wake the caterpillars up.”

That will happen in March or April, Taran said.

Taran says he has been successful establishing breeding populations of the Baltimore Checkerspot and the Regal Fritillary. He is hoping for the same success establishing a new population of the endangered Swamp Metalmark.

There are 20 to 50 caterpillars in each glass, and four glasses per flower pot, meaning 50 terracotta flower pots will be upended on the roof of the nature museum until next spring.

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