ELGIN -- There's a firm date to reintroduce endangered butterflies to Illinois.
The Swamp Metalmark butterflies were bred at the Peggy Notebaert Nature Museum's in Chicago by museum biologists.
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It took six years to prepare for the day as biologists grew the population in the museum's conservation lab. And the museum says the butterflies will be released Monday in suburban Elgin.
They'll be let loose at the 100-acre Bluff Spring Fen. It features wetlands, woodlands, prairies and savannas with mineral-rich water in its springs and streams. It is considered an ideal habitat for rare and endangered species.
The Swamp Metalmark is known for its reddish-brown wings that are lightly checkered.