An ominous, dense fog rolled over south Stock Island on Thursday morning, and it wasn't from Mother Nature.
The Florida Keys Mosquito Control District broke out the big guns to battle the Asian tiger mosquito, which has set up a stronghold in the mangroves of Stock Island.
A Mosquito Control spray truck treated the mangroves with a thicker-than-usual cloud called a "thermal fog," Mosquito Control spokeswoman Coleen Fitzsimmons said.
It contains the same active ingredient coming out of the regular Mosquito Control spray trucks, pyrethrin, but is mixed differently to linger longer over dense, wooded areas, known to breed this type of mosquito, Fitzsimmons said.
Mineral oil is added to the pyrethrin to make the fog denser, she said. The mixture is heated up, creating a thick fog that hovers 10 feet above the ground and lingers for 20 minutes.
In recent months, Mosquito Control has ramped up its efforts to eradicate the tiger mosquito on Stock Island, Mosquito Control Executive Director Michael Doyle said. The agency dispatched all its available Lower Keys field inspectors, armed with "backpack" fogging machines, to fight the species. They are also using a "barrier spray," a pesticide liquid sprayed through an airbrush-like device that coats the inside of sheds and the outsides and underbellies of homes, Doyle said.
He has called the efforts an "all-out assault."
The district has been working with the Navy Entomology Center of Excellence in Jacksonville on training field inspectors in thermal fogging, as the Navy is familiar with the technology, Doyle said.
The fog will be used on a very limited basis, because it is too thick to spray all the time, countywide.
"It's a backup plan," Doyle said. "It's a traffic hazard. It's opaque. You can't safely drive through, it's so thick."
The Asian tiger mosquito invaded Big Pine Key and Key Largo three years ago, and Stock Island in the early 2000s, Doyle said.
The species is "more irritating than Aedes aegypti," commonly found in the Keys, as it will bite anything with blood, he said. However, it is not a good carrier of dengue fever, a tropical virus that can be fatal. It does have the potential to carry dengue, but because it bites so many different animals, it would not likely carry it, Doyle said.
The insect is called a tiger mosquito because of its striped appearance. The mosquito has black and white striped legs and a small black and white striped body.