Lake Placid and surrounding areas are reporting an “unusually abundant” blackfly population in 2023, despite the widespread application of a pesticide that’s meant to kill blackfly larvae before they can turn into the flies that feast on human blood.

The town of North Elba has had a town-wide Black Fly Control Program since 1994. Town crews spray a small concentration of the insecticide BTI — or Bacillus thuringiensis israelensis — into moving streams located within the program’s 100 square-mile treatment area to kill blackfly larvae that are hanging around on the waters’ surface, nipping the problem before it’s hatched. The spray has a 90% to 100% efficacy rate. But this year, Black Fly Control Program Director John Reilly said warm and windy weather patterns gave blackflies across the North County a leg up on the BTI treatment.

BTI treatment is permissible within the Adirondacks because it’s a naturally occurring bacterium found in soils that specifically targets blackflies, according to Reilly, and the pesticide doesn’t persist in the environment long after it’s applied.

BTI has no toxicity to humans and is commonly used in organic farming practices, according to the U.S. Environmental Protection Agency. There is no documented resistance to BTI, according to the EPA, meaning black fly larvae aren’t growing impervious to the continued use of BTI. BTI was first discovered in Israel in the late 1970s and was first introduced to the Adirondacks in 1982, according to Reilly.

North Elba is just one of 24 municipalities and associations in the park that spends annual budget funds to suppress blackfly populations through the application of BTI, according to the state Department of Environmental Conservation, which issues BTI treatment permits. This year, North Elba budgeted $112,965 for insect control, Wilmington budgeted around $20,000, the town of Keene budgeted $31,000 and the town of Jay budgeted $18,800.

While Wilmington, Jay and Keene don’t have their own blackfly programs like North Elba, they all contract Kathy Vanselow, of Gansevoort-based Bioconservation, Inc., to treat waterways in their towns. Town of Jay Supervisor Matt Stanley said he hasn’t noticed an increased blackfly population in Jay this year, but Wilmington town Supervisor Roy Holzer and Keene town Supervisor Joe Pete Wilson Jr., like officials in North Elba, are reporting an abundant blackfly population this year.

“This is by far the worst I’ve seen it in quite some time,” Holzer said.

Warmer weather in April meant that more blackfly larvae hatched at the same time, according to Reilly, and a windy May could have blown in some flies from outside the BTI treatment areas in the park. Reilly said that climate change seems to bring blackfly season on earlier in the year, but he doesn’t believe a warming planet is contributing to an increased number of blackflies this year. It’s normal for blackfly populations to fluctuate from year to year, he said.

“I do worry about higher sustained winds in springtime affecting our treatment area,” he said.

And this year in North Elba, 33 private landowners in the town have denied blackfly field technicians’ requests to treat waterways on their property. Reilly said that’s a “slight increase” in denied requests compared to previous years.

“I dare not speculate why they chose that option,” Reilly said when asked why people denied BTI treatment on their property.

About half of the town’s total BTI treatment area — which includes around 250 miles of waterways — is on private land, according to Reilly, while the other half is on state land.

The good news in the town of North Elba is that the first round of BTI treatment is kicking in and reducing the first hatch of blackfly populations, according to Reilly. After a waterway is treated with BTI, North Elba’s field technicians return to the waters to check the efficacy of their treatments. If needed, field technicians apply another dose of BTI. Waterways are treated between two to 10 times per 15- to 17-week treatment season, as needed.

To reduce contact with blackflies, Reilly suggests wearing light-colored clothing, applying bug repellent and avoiding perfumes or colognes. Reilly prefers bug repellents with lemon eucalyptus oil.