Rain not to blame for mosquito boom
It sounds like an entomological contradiction: Southwest Florida has been virtually rain-free since May 16, and mosquitoes have been making life miserable this week for people in some areas.
But, contrary to popular belief, rain doesn’t always trigger mosquito breeding in Southwest Florida, and lack of rain doesn’t always mean a lack of mosquitoes.
“I think they’re worse than they’ve ever been,” St. James City resident Mike Grainger said. “It’s bad. They get in a cloud, 15 or 20 of them at a time flying in front of you.”
At the other end of the island, in Bokeelia, Jim Patterson agreed.
“They’re intense,” he said. “When I take my dogs for a walk in the morning, I’ve got to dress in long jeans, a long-sleeve shirt with the collar up and a hat on, and they still try to get up my nose and in my ears. If you wear flip-flops, they’ll eat your toes.
“The thing is, we haven’t had any rain. Where are they coming from?”
Like many people, Patterson thinks that rain drives mosquito production: Rain creates standing water; mosquitoes lay eggs in the water, and, boom, a swarm is born.
That’s not necessarily the case.
Mosquito species can be divided into two types: Old-water and new-water mosquitoes.
Old-water mosquitoes do, indeed, lay eggs on standing water — shallow pools, ditches, bromeliads, old tires, bird baths and so on — and rain provides standing water.
“Water must be standing five to seven days before we see rain-driven freshwater mosquitoes,” said Shelly Redovan, spokeswoman for the Lee County Mosquito Control District.
Because Southwest Florida has been so dry, though, when 1.5 inches of rain fell May 15, it soaked into the ground, so the old-water mosquitoes had no place to lay eggs.
New-water mosquitoes, — freshwater and saltwater — lay eggs on dry, flood-prone ground, and those eggs hatch when covered by water.
Freshwater new-water mosquitoes prefer places such as North Fort Myers, where sheetflow moving south from Charlotte County after heavy rains can cover the eggs.
“They also like the improved pasture lands around Alva,” Redovan said. “We haven’t had any rain, so those areas haven’t had a hatch-off.”
Saltwater new-water mosquitoes lay eggs on dry ground in coastal areas such as mangrove swamps, and those eggs hatch when tides cover them.
Recent extreme high tides associated with the full moon of May 17 have covered saltwater new-water mosquito eggs, which is why mosquitoes are in coastal areas.
“Rain is not the only factor,” Redovan said. “The big difference between us and up North is we’re more heavily impacted by tidal conditions.”
Mosquito control personnel trap and count mosquitoes throughout Lee County to determine where to spray. When they catch 50 in a trap, the district sends a truck to spray; when they catch mosquitoes in the hundreds, they send aircraft.
Recent trap numbers include Lehigh Acres with seven mosquitoes, Boca Grande with 78, Bokeelia with 135, Captiva with 283, and St. James City with 1,348.
Forty-eight mosquito species inhabit Lee County, and saltwater new-water mosquitoes are the most common.
Aedes taeniorhynchus is the species doing most of the biting this week.
Also known as the black salt marsh mosquito, taeniorhynchus is a nasty biter that can fly up to 20 miles for a meal.
This week, mosquito district aircraft hit both ends of Pine Island, Estero, southwest and northwest Cape Coral, and were scheduled to spray the outer islands, Bokeelia and Iona, on Friday night.
Although the district has had to eliminate some positions due to budget cuts, it has not eliminated positions essential to fighting mosquitoes, Redovan said.
The greatest hindrance to fighting mosquitoes is the fact that the district is not allowed to spray for adults on state and federal land.
“Mosquitoes don’t like to be crowded: They don’t stay where they hatch,” Redovan said. “So we go out and spray, and the next day, they migrate in from state and federal lands.”
Lee County isn’t alone in its mosquito infestation.
“We’re getting a similar kind of thing,” said Frank Van Essen, executive director of the Collier County Mosquito Control District. “We’re just starting to see the salt-marsh mosquito activity because of the tides.”
Al Hoffer's South Florida Pest Blog 