An annual sign of the arrival of summer, it happens slowly, and seemingly overnight. Along the course of the river, curious little white blotches appear on box elder and sycamore leaves, on the undersides of mighty sycamore trunks, and on the vertical faces of large rocks. At first, they are few and far between. By mid-summer, they can be spotted in vast colonies in suitable locations.
I first noticed them early in the summer. A lone white splotch resembling bird poop marked a sycamore leaf along the South Fork of the Shenandoah River, and I wrote it off as such. That is, until I began seeing them populating the undersides of branches and tree trunks. Quite confident in my belief that bird poop doesn’t defy gravity, I began to dig deeper. I quickly discovered that what appears to be the droppings of some riparian bird is in fact a clue pointing to one of nature’s many silent dramas.
The Eastern Dobsonfly
This silent, summertime drama begins (or ends) with the eastern dobsonfly. One of the United States’ largest non-lepidopteran (moths and butterflies) insects, the dobsonfly is a regular character spotted hanging around barn and porch lights on summer nights. Ranging from four to six inches in length, the dobsonfly is a dramatic-looking bug. Females sport short, but fierce and powerful mandibles capable of drawing blood from anyone unlucky enough to earn its wrath. Males are the most dramatic-looking of all, flaunting large, sickle-shaped mandibles that are incapable of delivering a painful attack.
In the absence of an attractive porch light, dobsonflies spend most of their short lives—which span just three days for males, and about 10 days for females—in riparian vegetation. It is here that, under the cover of darkness, the females lay their eggs on the undersides of tree trunks, leaves, and other surfaces suspended over the river. The eggs are layed in clusters of about 1000 and covered with a clear fluid excreted from the tip of the female’s abdomen, which dries to a pasty white color. The end result is a white blotch that resembles bird droppings about an inch in diameter.
Within a few weeks of being deposited over the river, dobsonfly eggs will hatch, and the larvae—a popular, and extremely effective, bait for our beloved smallmouth bass—fall to the water’s surface and float with the aid of an air bubble until they find a riffle comprised of cobble rocks in which to live.
Hellgrammites live in the larval stage of development for up to three years, feeding on small aquatic macroinvertebrates, and molting up to a dozen times as they grow.
In the early summer, with the arrival of the first summer thunderstorms, hellgrammites begin their “crawling”—exiting the river and crawling up onto the bank, seeking out a moist environment where they can pupate and begin their metamorphosis into an adult dobsonfly.
When the larvae find a suitably moist site—typically under a riverside log or rock—they dig a hole to serve as a cocoon with their powerful abdominal legs and mandibles, where they spend up to two weeks in the pre-pupal stage before molting into a true pupa. They spend up to another two weeks as a pupa underground before emerging as an adult damselfly, ready to repeat their life cycle with the few days of life they are given to do so.
As short-lived and good flyers as they are, adult dobsonflies, if a relevant food source at all for smallmouth bass and other river fish, are only a momentary one.
On the other hand, hellgrammites, the larval form of the eastern dobsonfly, are present in the benthic environment at all times. They are incapable swimmers and a dense morsel of protein. Thus, they are an effective bait and prized meal for the smallmouth bass.
For this reason, as I spend every day now rowing a boat down a warm water river in the summertime, I am made excited by the dense colonies of dobsonfly eggs on the undersides of the sycamore trees lining the river. It’s the height of bug season, and though my thoughts rarely proceed enthusiastically past visions of big smallmouth sucking down a helpless topwater imitation on a day-to-day basis, the promise of a bumper crop of hellgrammites in years to come reignites my appreciation for the ghastly bugs, and keeps me up at night perfecting imitations for every angling situation.