By Victor Greto
DOVER – The Depression-era work program was designed to get rid of the mosquitoes that made life south of the Chesapeake & Delaware Canal nearly intolerable.
What the program did instead was further propel the decline of the bay’s salt marshes, which already were reeling from pollution and diking.
The marshes were considered wastelands back then, says Bill Meredith, head of the mosquito control section of the state’s division of fish and wildlife.
To combat the mosquitoes, engineers designed a system called parallel grid ditching.
Young men, employed by the Civilian Conservation Corps, dug ditches 30-36 inches wide and as deep, spacing them in a grid pattern 150 feet apart. And they did it everywhere, not only on the shores of the Delaware Bay, but up and down the northeast coast.
Other species suffer
The point was to get rid of the standing pools of water in which mosquitoes love to breed.
Although it worked to a point, it also reduced the populations of marsh organisms that fed the fish, that fed the mammals, that fed the birds. That precipitated a decline in all species.
“In many areas, it got rid of large standing water bodies, but these were valuable habitats for water birds, and nursery areas for fish,” Meredith says.
Mosquitoes actually breed in only about 20 percent of the marsh area, but the ditches were dug throughout.
The widespread digging reflected, Meredith says, “an engineering attitude, not an environmental understanding of how the wetlands work.”
Workers also sprayed heavy fuel oil on the mosquito larvae to suffocate them. The oil, of course, also smothered surrounding organisms, depriving them of the oxygen they needed to survive.
Many of these practices continued for decades. The ditches dug in the 1930s were cleaned of silt 20-30 years later.
Still prime breeding grounds
“It wasn’t until the mid-1960s, when society became better attuned to the environment, that this changed,” Meredith says.
Many of the ditches are being silted in, and eventually will be reclaimed by the marsh.
Delaware’s salt marshes remain prime breeding grounds for mosquitoes, but the infestations of today are nothing like the ones recorded decades ago. During the early part of the 20th century, it was not unusual during bad infestations for 50-100 mosquitoes to land on a person in a minute.
Today, Meredith says, “We hire biologists who identify the [mosquito breeding areas] and that’s where we send our equipment. It’s selective placement of ponds and ditches, and we have no attachment to the tidal portion, which would de-water the marsh.”
You can reduce them radically, Meredith says, but because of the nature of the bay and the ecology of salt marshes, they always will be a problem. Although a small state, Delaware is in the top 10 for both human population density and wetland concentration.
“That’s an unholy mix,” Meredith says. “The wetlands produce a lot of mosquitoes.”