Biologists waded through knee-high vegetation in Florida until they reached a spot where purple flowers grew in cone-like formations — then the team got out the glow-in-the dark caterpillars.

The Florida Fish and Wildlife Conservation Commission announced April 30 that biologists had released caterpillars of the frosted elfin butterfly in Ichetucknee Springs State Park earlier in the month.

“This handsome butterfly is now rare or has disappeared from most of its historic range in the eastern U.S. and southern Canada,” the FWC said in a news release. “Florida has the largest remaining population in the Southeast.”

The release of the caterpillars, which glow under UV light, has been years in the making.

“Using wild-caught elfins from the Florida Panhandle, a captive breeding program was established at the Florida Museum of Natural History to produce individuals to release into good — but elfinless — habitat in north Florida,” officials said.

FWC staff visited the popular springs about an hour’s drive from Gainesville to deposit the small, green caterpillars onto their host plant, the purple sundial lupine.

Biologists waited until the caterpillars were old enough that they were nearly ready to begin metamorphosis, then they placed them onto the plant to eat and shortly after choose a leaf to build a chrysalis.

Once the caterpillars were placed, the team put up a mesh enclosure around some of them to see whether that will help them survive.

They will spend about nine months in the in-between stage transitioning from caterpillar to butterfly before emerging next spring, according to the FWC.

Surveyors will look to see if they emerge next year from February to April.

Biologists are carrying out these efforts as the species is being considered for protection under the Endangered Species Act.

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