Adirondacks’ battle against black flies: Bt’s role and debate over its use

The black fly has long been reviled in the Adirondacks. But is it time to declare a truce?

By Tim Rowland

In the middle of the 19th century, disease wiped out great colonies of European silkworms, causing garment manufacturers to turn to the reclusive island of Japan for a source of silk. The silk trade inevitably introduced silkworm mortality to Japanese shores as well, where in 1901 a scientist by the name of Shigetane Ishiwata tried to figure out what was going wrong.

His research, according to the National Library of Medicine (NLM), focused on a bacterium from dead silkworm larvae, information that was useful to the German scientist Ernst Berliner, who isolated a related strain from dead Mediterranean flour moth larvae he found in a mill in the German state of Thuringia. He named it Bacillus thuringiensis — Bt.

Q and A courtesy of the Environmental Protection Agency

Q. What is Bt?

A. Bti is a biological or a naturally occurring bacterium found in soils. It contains spores that produce toxins that specifically target and only affect the larvae of the mosquito, blackfly and fungus gnat. EPA has registered five different strains of Bti found in 48 pesticide products that are approved for use in residential, commercial and agricultural settings primarily for control of mosquito larvae.

It took another 25 years for science to figure out that the proteins in Bt, which occurs naturally in the soil, made for an effective insecticide by preventing hatches of problematic insects, including mosquitos and flour-eating moths. (Other, non-insecticidal proteins in Bt are toxic to some forms of human cancer cells.) 

Bt was first registered as an insecticide in the U.S. in 1961, and has been genetically introduced to crops since 1996, greatly reducing dependency on chemical insecticides, according to the NLM. 

Ernst Berliner had presumably never met an Adirondack black fly, but his discovery is now knitted into the culture here, as every spring, town employees and contractors sallie forth into sundry rivers and streams to apply Bt in order to keep the marauding hordes at bay.

When we bought our Adirondack property in 2014, the first person we heard from was not the welcome wagon, not the assessor, not any favor-currying politician, it was from the black fly combatants who somehow found us in our Mid-Atlantic home and wrote seeking permission to apply Bt in the flowing waters of our soon-to-be new home.

Bt was very familiar in that region, because it had been sprayed from small planes over eastern forests to prevent a serious infestation of gypsy (now spongy) moths. This was the 1980s, in the days when people were still convincible, so state Departments of Natural Resources were able to dispel any concerns.

Q. Does Bt pose a health risk to humans?

A. No. Bti has no toxicity to people and is approved for use for pest control in organic farming operations. It has been well tested by many studies on acute toxicity and pathogenicity (and) based on these studies, EPA has concluded that Bti does not pose a risk to humans.

Yet today in the Adirondacks, Bti — the added i refers to the israelensis strain most effective against gnats, mosquitoes and black flies — isn’t entirely without controversy, witness a recent Explorer story by Chloe Bennett on black fly treatments, which garnered more than 100 impassioned social media comments, voicing concerns for human health; the relative value of black flies as a food source for birds and fish; its potential to harm “good” insects; and, in a more cultural vein (this is social media, after all), whether black fly defense should be a matter of personal responsibility and the common refrain that real Adirondackers certainly should be able to shrug off a few bites. 

Q. Is Bti harmful to wildlife including honey bees?

A. Studies indicate Bti has minimal toxicity to honey bees. Bti produces toxins that specifically affect the larvae of only mosquitoes, black flies and fungus gnats. These toxins do not affect other types of insects including honey bees.

Bites aside, black fly strains (there are thousands worldwide) in this neck of the woods pose no particular risk to humans through the transmission of disease. Stagnant water is often blamed for insect infestations, but black flies need running water to thrive. The larvae knit something of a silky sling on rocks or sticks and hook to it with tiny barbs in their mid-section, letting the current deliver their meals. It is the female that bites, because she needs blood to produce eggs — male black flies can’t draw blood and demonstrate little interest in humans altogether.

Certainly no less an authority than Adirondack Murray — whose writings introduced many city slickers into the howling wilderness in the 1800s — felt black fly phobia was overblown. Black flies in his view were “one of the most harmless and least vexatious of the insect family … a monster existing only in men’s feverish imaginations.”

He then went on to describe how a few simple precautions against the insect could negate the threat, which involved wrapping oneself in so much fabric it would have made mummification look like a string bikini.

In the Adirondacks black flies are pest, it is true, but they are also a totem, a seasonal signpost and even, dare we say, a matter of pride. While people in other locales make note of the first robin of the spring, the first daffodil, the first peeper, we duly mark the commencement of the season with the first black fly. Sitting atop Buck Mountain in North Hudson on Friday, April 26, my brother Bruce called out, “Black flies!” He’s enough of an Adirondacker to sound (almost) happy to note their return. And by now, I’m enough of an Adirondacker to not even have noticed.

Q. Does Bti pose risk to crops or water supplies?

A. No. Bti has no toxicity to people, so it can be applied safely to mosquito habitat without a detrimental impact on food crops or water supplies. In fact, Bti can be used for pest control in organic farming operations. There are multiple Bti products and some are allowed to be used on certain drinking water (e.g., cisterns) while others are not intended for that use.

That brings up another issue, which was pounded on social media until it bled: Are Adirondackers tougher/less susceptible to blackfly bites than tourists? And what’s the definition of a real Adirondacker anyway? “Y’all have no idea,” drawled one poster after coming under attack. “Our family owns 156 acres of Adirondack land. I have been hiking, canoeing in the ADK since the mid 70s! But of course y’all became experts because you shop at LL Bean.”

Using the word “y’all” to express Adirondack bona fides is like putting your poutine on a bed of collards, but the point is taken, particularly as blackflies are part of a broader Adirodack lexicon, lending their name image and likeness to things like whiskeys, festivals and mountain bike races.

But serious Adirondackers also know that there are black fly attacks and then there are Black fly Attacks.

According to Purdue University, black flies in untreated areas can become so severe that outdoor activities are basically impossible, and in some extreme cases have been fatal to animals. Milk and egg production can be negatively affected by black flies, and in Pennsylvania, the Department of Environmental Protection notes that a bad season of black flies has a  measurable negative effect.

Q. Are there special precautions to be taken during Bti spraying?

A. No special precautions are needed for applying Bti. A number of Bti products are sold as “homeowner” products and are easy and safe to use. People do not need to leave areas being treated.

Before Bt was introduced to the Adirondacks in 1982, individuals were left to battle the lawless insects for themselves, and came up with an inspired directory of home brews with ingredients including ammonia, Vaseline, turpentine, olive oil, pine tar and such.

Black flies are attracted to darker colors and carbon dioxide, so to minimize their impact, wear light clothing and don’t breathe.  

Bt and the chemical DEET (the active ingredients in most bug sprays) have battled black flies to at least a draw, but human comfort isn’t the only consideration. Rich Redman, former president of Trout Unlimited, said the great fly-fishing guru Fran Betters of Wilmington was among those who recognized the value of the black fly to the ecology. “Kill the larvae and you decrease the food source,” Redman said. “All to keep the tourists happy and spending money in Lake Placid. If they really want to experience the Adirondacks, then they can deal with the bugs just like the rest of us do.”

Are insects becoming resistant to Bti? 

No. There is no documented resistance to Bti as a larvicide. A recent study confirmed previous research showing a lack of Bti resistance in mosquito populations that had been treated for decades with Bti.

The Pennsylvania DEP agrees that “Black flies play an important role in aquatic and terrestrial food chains where they are preyed upon by many insect predators, fish, amphibians and birds.”

And “black flies are important filterers of our waterways,” wrote naturalist Ellen Rathbone in the Adirondack Almanack. “In fact, when water gets too full of organic matter or nutrients, the amount of dissolved oxygen decreases and very little can survive in it. Blackfly larvae are indicators of good, clean water.”

So there you go, blackflies are good for the ecology — except …

I asked Derek Rogers, an avid birder and member of the Adirondack Land Trust, about blackflies’ value as an avian food source, and his research also turned up a 2014 story from the Minneapolis Star Tribune stating that “Common loons have joined whooping cranes as iconic birds under attack by black flies this year. The tiny, voracious, biting insects are driving those birds off their nests, exposing eggs to loss.”

Oh well.

Black flies are a complicated issue. We’ll leave it to Rathbone, who probably sums it up best: “While many of us would just as soon not have to deal with another black fly, we should all remember that every living thing on this planet has its rightful place. It’s only when the delicate balance is thrown out of whack that problems occur. So, greet the black flies this spring with a smile.”

Black fly illustration by Mark Joseph Sharer