Adult blackfly illustration by Robin Rothman, courtesy of the New York State Museum
Make no mistake; I do my share of swatting during spring bug season. However, as a biologist, I do it with a touch of respect. While blackflies can be bothersome, spread disease, and repel tourists who support our local economies, they are also remarkably diverse, courageous, ecologically important and just plain cool.
The term “blackfly” refers to more than 2,000 species worldwide, and roughly 90 percent of the North American species never bite humans. Surveys conducted in the Adirondacks alone have identified more than a dozen species belonging to at least four genera. Most of our “hominoxious” ones belong to the genera Simulium and Prosimulium, although some of those species are more likely to bite than others. For instance, S. jenningsi and S. fibrinflatum may swarm you for a sniff, but they normally prefer the blood of other mammals or even birds.
Why do they bite us at all? Typical adult blackfly cuisine is plant sap and nectar, and the males consume nothing else. Adult females of the biting species, however, seek more nutritious fare to supply the eggs developing within their bodies, and they risk death to do so. We may glorify mythical heroes like Saint George or Siegfried for attacking mere dragons, but when scaled up to our size the Simuliid Amazons go after monsters who stand more than a thousand feet tall, know they are coming, and want to kill them. Hats off to those tiny Valkyries—if you don’t mind them in your hair.
Bacterial Bti sprays that we apply to streams in order to kill the aquatic nymphs before they mature can reduce populations by more than three quarters but leave most other organisms unharmed, which more broadly toxic pesticides of former times failed to do. Nonetheless, we don’t know exactly how we might affect ecosystems in doing so.
Any large population of insects represents a potential food source for other species. In the case of blackflies, we’re talking brook trout, aquatic worms and stream-dwelling insects such as juvenile caddisflies, midges and stoneflies who eat the nymphs, and the adults later fall prey to dragonflies, amphibians, spiders and birds. In that sense blackflies are ecological conduits between the realms of the living and dead. With the aid of bristly mouth-brushes the nymphs sweep up tiny particles of plant, animal and microbial matter that death and decay release into the streams, weaving their edible elements into blackfly bodies that, in turn, support their predators on land as well as in the water.
Most research concludes that the effects of blackfly control on food webs are minimal, perhaps because most animals who dine on blackflies feed on other species as well. But those studies are few in number, and some do indicate unintended consequences. One such investigation showed that blackfly removal decreased the abundance of dragonflies and midges which, in turn, reduced the survival rates of local insect-eating swallow chicks by one third.
The affected regions are also potentially large, because the winged adults disperse widely. In one Adirondack study, thousands of adult flies were dusted with brightly colored fluorescent powder, released, and recaptured as many as four miles away. Amazingly, the great distances covered were not simply due to hitchhiking on strong breezes; most of the recaptured individuals had flown upwind, presumably in search of new breeding or feeding grounds.
The Environmental Protection Agency and other reputable sources report that Bti is toxic only to blackflies, mosquitoes and gnats, but that is not strictly true. Bti has also been shown to kill zooplankton and non-biting midges who are themselves important food sources for newts, fish and other predators. We simply don’t know the full ecological impacts of Bti treatments because of a general shortage of scientific information on the countless insects, worms, microbes and other small life-forms who comprise most of life on Earth, many of whom have yet to be listed as present in the Adirondacks much less studied for sensitivity to blackfly control measures.
Will climate change affect our interactions with blackflies in the future? As summers grow longer and warmer, we might see some species extend their geographic ranges northward. Pennsylvania has more than 50 species of blackfly, some of whom might become more common here eventually. Fortunately for us (and for Pennsylvanians), few of them bite humans. On the other hand, longer summers might allow some of our local biters who now produce only one generation per year to breed more often and grow more numerous. Only time will tell how bug seasons ultimately change as the world warms.
No mammal enjoys being fed upon by micro-vampires, and being mammals ourselves we need not feel too guilty about resenting some of our insect neighbors on occasion and taking appropriate measures. But let’s respond with caution and, yes, a measure of respect. After all, even pesky blackflies are fellow Adirondackers, too.
Playing Keep Away
According to Anne LaBastille, in “The Black Fly” (Summer 1974), “At the present time, the best relief from blackflies may be accomplished by staying out of the Adirondacks during blackfly season.” LaBastille also recommended locating campsites in airy, open, high areas, and dressing to minimize exposure—“avoid bikinis,” she wrote, “and fish-net T-shirts.”
George Washington Sears, aka “Nessmuk,” had his own 19th-century defense system, as he explained in Forest and Stream: “As for myself—even on Brown’s Inlet—they pass me by as if I were a hot griddle. On starting in I established a good, substantial glaze, which I am not fool enough to destroy by any weak leaning to soap and towels.” His recipe for insects: “three oz. pure tar, two oz. castor oil, one oz. oil pennyroyal. Simmer together thoroughly, apply copiously, and don’t fool with soap and water till you are out of the woods.”
Some other schemes? Stay indoors on days of high humidity or, if you must venture out, use a smudge pot or build a smoky fire. And William West Durant favored a pricier option: he had a 60-by-26-foot houseboat called The Barque of Pine Knot built that he’d float to the center of Raquette Lake during blackfly season.
For the bug-dope do-it-yourselfer, Wallace’s Descriptive Guide to the Adirondacks (1887) offers these homemade options.
No. 1—½ oz. of oil of pennyroyal poured into 3 oz. of melted mutton tallow. Lard is sometimes used, but it is too soft and is not as healing.
No. 2—6 oz. mutton tallow, 2 oz. camphor, 2 oz. penny–royal, ½ oz. creosote (or carbolic acid solution).
No. 3—4 oz. glycerine, 2½ drs. oil of peppermint, 4 drs. spirits of turpentine.
No oil of pennyroyal handy? No worries. Pure Placid (www.pureplacid.com), based in Lake Placid, makes Shoo-Fly, a spray that repels mosquitoes, blackflies, ticks and deerflies, among other pests. Ingredients are natural and include rosemary, cedar, thyme, citronella, cinnamon, clove and lemongrass oils. Shoo-Fly also comes in a formula for dogs and other pets.
Adirondack-made Bye-Bye Blackfly (bye-byeblackfly.com) is also DEET-free and made from natural ingredients, but delivery is in the form of a salve with white beeswax as a base.
