Unwelcome as the plague but as inevitable as summer following spring, greenheads will soon make their annual visit to the region.
Greenhead flies appear in early July and are active for about three to four weeks, hatching in batches until early August.
The green-eyed, horsefly-sized insects don’t discriminate; they pester fishermen, kayakers, sunbathers and swimmers — in or out of the water — near the beach and salt marsh.
“They have jagged mandibles that saw into the flesh,” said Bill Mehaffey, supervisor at the Essex County District of Northeast Massachusetts Mosquito and Wetlands Management (NMWM), located in Newburyport. “While they’re biting, they secrete an anticoagulant so the blood won’t clot.”
Many communities in the region contract with NMWM in an attempt to control greenhead populations. Mehaffey and his crew are responsible for building, baiting and erecting the black and blue greenhead traps placed strategically around the region. After Labor Day, they also remove the traps, clean and repair them for reuse, if possible.
The color attracts the flies, Mehaffey said, and there’s some debate over whether black or a royal blue does that best. A chemical bait, octenol, is also used, and has proven to attract more flies in traps with it than without it.
“The bait smells like bovine breath, because these flies love cattle and the smell attracts them to the traps,” Mehaffey said. “We also spray Bti, from a helicopter on the salt marsh. That’s a bacteria that affects the flies. It’s organic and environmentally accepted.”
There is an additional benefit when using Bti, which comes in 30-gallon drums, he said, for NMWM turns the barrels into more greenhead traps.
“Salisbury has the round barrels and they collect just as many flies,” Mehaffey said. “Salisbury puts out about 30 traps and they’ve all been placed. They’re in the salt marsh behind homes along (the west side of) Northend Boulevard. There are also a few in the reservation and others here and there. The state police have their horses stabled at the reservation. Horses are really bothered by the greenheads, and we put a couple there.”
Newburyport puts out 13 traps, he said, but by far Newbury, with huge stretches of salt marsh, is the community most heavily invested in greenhead traps, putting out 87.
At about $70 each, costs mount up.
Some seasons are worse than others when it comes to greenhead volume. Last summer there were reports that there were fewer greenheads than usual, he said, but other years, the numbers have soared.
“They like hot, steamy weather and it’s the first brood hatching that can be the worst. That comes around the 4th of July,” Mehaffey said. “Old timers say if there’s a full moon high tide that floods the marsh around that time of the first hatching that it can sweep them away. So let’s hope that happens this year.”
As far as how to keep the greenheads from biting, Mehaffey doesn’t know of any surefire solutions, although he does believe from experience that wearing light clothing and covering up helps.
Some recommend using insect repellent containing DEET, but Mehaffey advises caution when doing so.
“Different repellents have differing concentrations of DEET, and I wouldn’t put the ones with high concentrations of DEET directly on the skin, especially with children,” he said.
There are those who recommend horsefly repellent — usually found at garden supply stores — and others who suggest wearing Avon’s Skin-so-Soft bath oil as a way to keep the flies at bay, he added.
“I don’t have any experience with Skin-so-Soft because I’ve never used it,” Mehaffey said. “But you can be driving down the road and come upon people sitting at a card table selling Skin-so-Soft. They swear by it, but I have no way of vouching for it.”