Adirondack towns roll out black fly defense

Warmer winter prompts communities to deploy Bti pesticide against black flies earlier than in past years

In late February this year, Andrea Malik looked around at open streams and bare grounds in the town of Colton and began to count down. Although it was still winter, the black fly program director knew waters in the area were unusually warm, allowing eggs to hatch. 

For 38 years, the so-called “black fly diva” has treated waters around Colton with the pesticide Bacillus thuringiensis israelensis (Bti) to kill larvae. The small juveniles grow into the biting insects typically known to swarm Adirondack forests throughout May and June. 

This year is different, she said. The team, which includes Malik and three others, normally start in mid-April. The technicians began treating streams at the beginning of March. 

“This is the earliest ever,” Malik, who also leads Bti training programs around the park, said.

The treatment is applied to streams as narrow as 4 inches wide to rivers like the Ausable. First discovered in the 1970s, the bacterium kills both black fly and mosquito larvae. Research shows Bti is generally not toxic to wildlife and humans. 

Permits for applying the pesticide are issued by the state Department of Environmental Conservation. Bti is the only pesticide allowed by the DEC on forest preserve for the control of biting insects, according to a landowner notice letter. 

More than a dozen towns in the park have Bti permits this year, public documents show.

In the town of Webb, black fly program director Jason Villiere said he wanted to start Bti treatment ahead of the date stamped on his permit but abided by the set rules. Water temperatures in the town and around Old Forge were warm enough the first week of March to begin. 

“This is unusual,” Villiere said. “Generally, we’ve been starting, in the last five years or so, maybe the third week of March if not more towards even April for us.”

As the climate changes, warmer temperatures are causing mild winters that disrupt natural cycles for insects like black flies. Eggs laid in the fall hatch in streams once water temperatures reach about 50 degrees. Larvae numbers are average in towns the Explorer reached. 

North Elba began treating waters a couple of weeks early this year, black fly program director John Reilly said. The winter warm-ups and thaws shifted Bti application times from early April to mid-March. 

Malik said the appearance of ticks is also a concern as winters become more mild. About 10 years ago, the program invested in permethrin-treated clothing to repel the bugs. 

“I used to run around in the grass, roll around in the grass, I don’t dare doing that now,” she said. 

The warming from El Niño this year likely contributed to temperatures this season, though Malik said she noticed gradual warming over the nearly 40 years she has spread  Bti. 

Malik recalled a time about at least a decade ago when she skied on a river under a full moon in mid-March. Snow and ice covered the ground and black flies were far from her mind. Now, late winter looks different in Colton. 

“We don’t have the winters we used to have,” Malik said.