APPLE VALLEY — The 20 tiny butterfly larvae being cared for by a Minnesota Zoo biologist could represent the last hope for a species that used to be ubiquitous across the state’s prairies.

The Poweshiek Skipperling used to flit and float above more than 2 million acres, but for reasons that aren’t entirely clear they’ve virtually disappeared.

“They just fell off the map. It may already be extinct in the state,” said Erik Runquist, the Minnesota Zoo conservation biologist who leads its butterfly conservation efforts.

The Poweshiek, a brown butterfly with white stripes, is about the size of a quarter as an adult. It hasn’t been seen in the state since 2007, and its near-extinction suggests that the butterfly’s habitat is ailing.

“When you consider the prairie ecosystem, and things start dropping out, something is not right,” said Robert Dana, an ecologist with the state Department of Natural Resources.