Changing climate gives mosquitoes more time to live each year

Apr 18, 2024

Partnership Journalism•July 10, 2023

By Bill Barlow (Press of Atlantic City). Priyanka Runwal (Climate Central) contributed reporting.

This is the first story in a two-part collaboration between Press of Atlantic City and Climate Central examining connections between climate change and mosquito hazards

Michael “Gus” Gustray, an Atlantic County biologist, watched as helicopter blades picked up speed, blowing back the dry grass before the chopper lifted off on a search-and-destroy mission, banking over a line of trees and heading toward the wide expanse of salt marsh.

The target: Tiny insects that can weigh as much as 2½ grains of table salt.

The Centers for Disease Control and Prevention calls the mosquito the world’s deadliest animal because the diseases they spread kill hundreds of thousands worldwide every year.

In addition to that, they are very annoying.

Because of the heat-trapping effects of fossil fuel emissions, they are also here longer. By analyzing temperature and humidity trends from a station at Atlantic City International Airport, science and news group Climate Central found the mosquito season here is 23 days longer on average than it was in 1979.

“From what we are seeing, that’s fairly accurate,” said Doug Abdill, the superintendent of Atlantic County’s anti-mosquito efforts. “It’s not like one kind of mosquito is living longer, but there are more days in the year that are suitable for a mosquito to be alive.”

In practical terms, there are now more than five months of every year on average when weather conditions in South Jersey are conducive to mosquito bites. And if West Nile virus or any of the other diseases they spread are circulating, each bite can bring a severe health risk in addition to an itchy bump.

Which one is which?

Patrick McGrath, an identification specialist with the Atlantic County Office of Mosquito Control, said staff members start checking water temperatures in March. When the water gets to be about 55 degrees, mosquitoes become active enough to start to breed.

The most intense activity comes in June, July and August, but the mosquitoes have been around longer and longer in recent years, as shown in mosquito traps placed around the county.

“We were ending up around the middle of October, when it started to get cooler. Now, we’re doing these collections longer. We’re doing them into November now,” McGrath said.

He and Gustray, a biologist with the department, were in the county’s mosquito lab in the basement of a small, nondescript building at the county’s public works yard off Dolphin Avenue. There’s a flat-bottom outboard boat on a trailer outside with the Atlantic County seal and the words “mosquito control,” but no other indication that this is mosquito central for the county.

McGrath had a tiny mosquito under a microscope, one of those caught in a light trap. The device looks like a well-made birdhouse, with wooden sides and a metal roof. The light attracts mosquitoes, which are then caught and contained.

Gustray shows off some of the other tools, including one that uses stinky standing water in a black plastic tray. When a mosquito comes in to lay its eggs, a surprisingly gentle fan blows it into a container set above the water. Yet another trap uses dry ice to create carbon dioxide. For a mosquito, carbon dioxide is an indication that something is exhaling, and where there is breathing, there is blood.

Earlier that day, Gustray watched as the helicopter took off from the open field at Stillwater Park at Shore Road. The county office does not own a helicopter but at times rents one to reach remote areas such as in the salt marsh, sometimes in cooperation with the state mosquito program.

In Atlantic County, the office of mosquito control falls under the county Department of Public Works. Its job is to cut back on the mosquito population, but also to understand what mosquitoes are out there and what dangers they present.

The team works with the state’s mosquito control program under the Department of Environmental Protection to watch for diseases and study mosquito populations.

There are 63 different mosquito species in New Jersey, and more than 40 of those have a home in Atlantic County.

When Gustray gives talks in schools or at community groups, he said, many express surprise that there are multiple species of mosquitoes. Many just assume a mosquito is a mosquito, he said. But there are complicated differences, including in what time of day they feed, where they reproduce and their preferred habitat.

Some prefer salt marshes, others standing fresh water. Some like stormwater basins, while some, including the aggressive Asian tiger mosquito, which can carry West Nile virus and eastern equine encephalitis, can lay eggs in the water that collects at the bottom of a potted plant tray or other small container.

In addition to other means of control, mosquito experts say pouring out any standing water around homes can make a noticeable difference in the mosquitoes in the air.

“If we could get people to understand the habitats, and just how little water they need to breed in, I don’t think we would have the amount of problems,” McGrath said.

After Gustray and McGrath identify the mosquitoes, they freeze some of them — mostly species most likely to carry diseases — to be sent to state labs for testing.

It’s about more than heat

While heat waves strike more frequently and severely now than they used to, and with humid heat becoming more common, such conditions alone don’t necessarily mean that summer skeeters will be unbearable this year.

As much as warmth, mosquitoes need water, McGrath said. Not only do they need it to lay their eggs, most species of mosquitoes tend to be more active on humid days than on hot, dry ones.

At Cape May County’s Mosquito Control Commission, Matt Diem, the assistant superintendent, said a drought can be extremely damaging to crops and wildlife — and to mosquito populations.

“They really don’t like it when it’s very low humidity,” he said.

Over the past two years, below-average rainfall kept down mosquito populations. There has been some rain recently, but Diem said it looks like this could be another dry, hot summer.

“I guess the perfect storm would be warmer temperatures and a wet summer,” Diem said.

Interviewed earlier, McGrath made the same point. Mosquitoes need water.

“If things start to warm up earlier and we have a crazy downpour, that’s a horrible recipe,” he said. “That’s what happened this year.”

While much of the year has been unusually dry, a single storm this spring dropped between 5 and 7 inches of rain as the weather warmed, fueling a mosquito outbreak.

Atlantic County’s mosquito control efforts began more than a century ago, at the beginnings of organized efforts to control mosquitoes, running through the famous pesticide trucks fogging streets with a mixture of diesel fuel and DDT, to today’s efforts with integrated pest management, in which Abdill said the team seeks to control the insects with as little impact on non-target species as possible.

Now, every county has its own mosquito control effort, coordinating through the state. Within that world, it’s accepted that warming temperatures are influencing what kinds of mosquitoes can thrive here and how long they will stick around.

“The evidence is there. You can’t refute that,” Gustray said.