Environment

Florida Keys says goodbye to flesh-eating screw flies

Endangered Key deer in fight for survival against screwworms

As of Friday afternoon, Oct. 14, 2016, 83 endangered Key deer had been euthanized because of an infestation of the New World screwworm. The screwworm, not seen in the U.S. since the 1960s, is leaving open wounds on the deer and then eating the fle
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As of Friday afternoon, Oct. 14, 2016, 83 endangered Key deer had been euthanized because of an infestation of the New World screwworm. The screwworm, not seen in the U.S. since the 1960s, is leaving open wounds on the deer and then eating the fle

About 190 million screw flies later, South Florida appears to be free of the flesh-eating pest that threatened to wipe out the planet’s last remaining herd of tiny Key deer.

On Tuesday, the U.S. Department of Agriculture will release its final sterile fly to combat an infestation confirmed in September, which marked the first outbreak in the continental U.S. in three decades. About 135 deaths in a herd numbering just 875 were blamed on the insect — formally known as the New World screwworm fly — although the numbers could be higher since the herd is spread across such a wide area that also includes remote back country.

In an interview with the Herald Monday, the USDA’s Animal and Plant Health Inspection Service chief veterinarian called the massive effort a success, despite the flies getting a head start.

Anytime you can eradicate a disease like this quickly, it’s a good thing.

Jack Shere, chief veterinarian for the U.S. Department of Agriculture Animal and Plant Health Inspection Service

“This is a real success story for Florida and for the fish and wildlife folks and the people in Monroe County,” Jack Shere said. “Anytime you can eradicate a disease like this quickly, it’s a good thing.”

U.S. Fish and Wildlife Service officials at the National Key Deer Refuge hope to slow the spread of the screwworm throughout the Key deer community by feeding the animals bread medicated with an anti-parasitic drug.

The flies, which lay their eggs in open sores so larva can feed on live flesh, probably arrived months before they were confirmed, Shere said. But because they are so rare in the U.S., they were overlooked as a source for the grisly head wounds on male deer heading into the fall mating season. That gave the flies time to establish breeding populations in the islands, and meant a much more intense response.

Altogether, Shere said flies were detected on 13 islands. While the agency typically uses aerial releases to treat big areas, the winds and geography across the Keys required ground releases. Every Monday, millions of chilled sterile larva arrived by plane from a U.S. breeding facility in Panama and were then warmed and released, ready to hatch and mate with wild flies. Enough flies were released to cover five life cycles, he said.

13The number of islands in the Keys where screw flies were found

Shere estimated that the USDA spent between $3 million and $4 million, which does not include state costs to man a checkpoint round the clock at Key Largo or the U.S. Fish and Wildlife Service expenses, which included treating and monitoring the deer.

Where the flies came from and how they arrived in the Keys remains unknown, although Shere said there are obvious suspects.

It takes just a couple of flies hitchhiking on a boat or a plane to get something like this started.

Jack Shere, chief veterinarian for the U.S. Department of Agriculture Animal and Plant Health Inspection Service

“It takes just a couple of flies hitchhiking on a boat or a plane to get something like this started,” he said. “And it happened at an opportune time, during rutting.”

The agency is continuing to try to track the source by comparing DNA in the Keys flies to DNA in flies throughout the Caribbean and South America, where they have not been contained. If they can identify the source, measures can be put in place, like spraying planes or more closely inspecting animals.

“The lesson learned is vigilance,” he said. “Early detection is really key to eradicating any disease, no matter what disease you’re talking about.”

Follow Jenny Staletovich on Twitter @jenstaletovich

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