Hoping to avoid what is intolerable, we seek shelter, wrap head, wrists, and ankles, apply evil-smelling concoctions, and sometimes employ a vocabulary best left unused in company. It is blackfly season, a time of attacks behind our ears, under watchbands, and down our socks. Picnics and dispositions are ruined.
But it’s only the adults that plague us, and then only the females.
An efficient bloodsucker, the awful adult female blackfly uses chemically sophisticated saliva to keep blood from clotting while she drinks her fill. It is this saliva that arouses our body chemistry to inflammation. Her sense of survival causes her to bite precisely where we are least likely to notice her presence. Then, with inflated body, she flies off to rest and digest the meal, an elusive little Dracula. The males? Inoffensively mild little creatures who sip nectar from flowers.
And at the larval stage, the blackfly deserves our admiration. Anyone examining a brook has seen them, not realizing their identity. Find a riffle where water flows over a flat rock before plunging into a pool. In swift water on the brink of that rock, dozens of dark, twig-like objects bend downstream from the force of the current, each a quarter of an inch long. They could be anything—plants perhaps. Look more closely.
Here is an elongated, brownish insect larva, club-shaped, with bulbous end attached to the rock. At the narrow upper end, two fringed appendages protrude from a small dark head. A circlet of hooks on the swollen bottom of the larva grip a mat of silk attached to the rock’s surface. This is the insect’s home plate.
The seed-shaped head has chewing jaws with scale-like teeth, a scattering of four simple eyespots, a pair of antennae, and those two specialized limbs. The tip of each of these appendages is equipped with a fan of about 50 curved bristles that unfolds in the flowing water. When an edible morsel is snared by the bristles, it is thrust into the mouth and swallowed. A brook may appear crystal-clear, but it transports enough organic matter to feed a multitude of inhabitants. Blackfly larvae have little to do but wait for a meal to arrive.
Harboring a grudge against blackflies, you dislodge a larva and watch it whirl away downstream to what you hope is oblivion. Be prepared for a surprise. A foot or two away, the little insect suddenly defies the laws of physics and stops dead in the racing water. Astonishingly, it begins to move slowly back upstream until it reaches its silken mat. Secure again, it extends head fans and begins feeding as though nothing unusual has happened. What miracle is this? When dislodged, it spins a silken lifeline, one end of which remains attached to the mat. From huge, body-long salivary glands, it pays out silk until safely out of harm’s way, then stops, grasps the thread in its jaws, and begins “reeling in” by eating the strand of silk. No wonder adult blackfly populations are so large: there aren’t many predators in a brook capable of catching their larvae.
The life stages of a blackfly resemble those of many insects. A female enters the water to lay 500 or so eggs, sometimes choosing instead a wet leaf along the stream bank. With a pointed “egg burster” on its head, each tiny larva soon hatches and creeps to find a place of attachment in the swift water. It feeds, molts up to nine times, and then, before transforming into a flying insect, enters a non-feeding stage, a blackish, hump-shaped little pupa inside a streamlined silken cocoon. Two sets of feathery gills trail downstream to extract oxygen from the water while metamorphosis takes place.
Transformation complete, the pupal case splits at the head and the new adult, encased in a bubble of air emitted from under its skin, whirls off downstream, instantly rising to the surface. The bubble bursts, and, with hairy, water-repellent feet, the tiny insect runs across the water to a plant or shoreline where it dries its wings and flies away—homing in on that vulnerable spot behind your ear (remember, only females do this). In its genes, a message developed over millennia of being swatted says that thin-skinned hairlines are safe places to find a meal.
Why not sing the praise of this scourge of the North Country, this remarkable creature with an obscure origin in upland brooks? Swat adults if you must. But if for no reason other than its extraordinary specialty for survival in a turbulent watery world, the larval blackfly is worthy of our wonder.