By Laura Myers

BAHIA HONDA STATE PARK, Fla., Nov 19 (Reuters) - The Miami blue butterfly, a fragile cornflower-hued insect no bigger than a thumbnail, was granted endangered species status on Wednesday by Florida officials.

The Florida Fish and Wildlife Conservation Commission, meeting in the Florida Keys, agreed to the classification that gives more formal protections to the last remaining colony in the United States.

About 45 to 60 Miami blues live in Bahia Honda State Park, a lush island of swaying palms and coral rock in the Florida Keys. Protection goals there include propagating the insects, which are fenced in at a special restoration area, to increase their number to more than 250 in the next 10 years.

"This is the only place in the United States where the Miami blue is found," a fervent Jeffrey Glassberg, president of the 5,000-member, New Jersey-based North American Butterfly Association told Reuters. "It's impossible to believe anything is more endangered any place on Earth."

The Miami blue, known as a Hemiargus thomasi bethunebakeri is a fast, erratic flyer with rounded wings. Both sexes have two "eye spots" on their underside outer margins, marked by wide white bands.

Florida's "endangered" designation maintains an existing ban on capturing the butterflies without a permit, and formally requires state wildlife officials to set up a program to stabilize and increase the butterflies' population.

A state emergency order, enacted in May, made netting, injuring or killing a Miami blue a third-degree felony, punishable with a fine of up to $5,000 and up to five years imprisonment.

The U.S. Fish and Wildlife Service is reviewing the Miami blue but has not decided whether to grant federal protection, spokesman Tom MacKenzie said.

The species was once prevalent as far north as Tampa on Florida's Gulf coast and Daytona Beach on the Atlantic coast, and is also found in the Caribbean.

The rapid U.S. decline of the Miami blue in the last decade is attributed to Hurricane Andrew in 1992, butterfly collectors, dry environmental conditions and "human-based mortality from pesticide and herbicide spraying," according to the state's Miami Blue Management Plan.

But entomologists at the Florida Keys Mosquito Control District dismissed as unfounded claims that mosquito spraying helped to kill off the Miami blue.