Download Stoneflies - Hickory Knolls Discovery Center

July 3, 2014
Stoneflies
It may seem, at first glance, that our Fox River Bugs are a pretty homogenous bunch.
I mean, really, how different could they be? Head, thorax, abdomen…two antennae, six legs,
wings… Glanced from the windows of passing cars, or even up close and personal on a
windshield or radiator grill, these often-plentiful insects all appear to share a certain sameness.
But talk to a naturalist, fisherman or anyone else passionate about streams and aquatic
ecosystems, and you’ll quickly learn that the various groups of River Bugs are as diverse as
ecological niches they occupy.
The Trichoptera, or caddisflies, are notable for their fanciful larval cases, their hairy little wings,
and their tendency to form dense mating swarms that weirdly coincide with river town street
festivals.
The Ephemeroptera, or mayflies, are famous for
their short adult lives and, in some circles, their
gorgeous colors, lacy wings and long, flowing
“tails.”
And then we have the Plecoptera, or stoneflies.
When outdoor enthusiasts speak of these River
Bugs—and we do, a lot—the conversation takes on
a completely different tone. Voices hush, and faces
take on a look of awed reverence. For stoneflies
are the Holy Grail of all River Bug-dom.
Like caddis and mayflies, stonefly juveniles, or
nymphs, are aquatic. But unlike their underwater
neighbors, most of which are tolerant of small
amounts of impurities, stoneflies are exceedingly
persnickety about their environment. They need
Stoneflies, even the common species, are increasingly hard to find
these days. This juvenile, also called a nymph, was found underneath a
rock in Ferson Creek at LeRoy Oakes Forest Preserve in St. Charles.
cool, well-oxygenated water with a rocky, unsilted substrate—habitat that’s hard to find in
developed areas. As a consequence, stoneflies are at the present time a rarity here in the
TriCities.
So you can imagine my surprise when, just the other day, our St. Charles Park District nature
camp kids discovered a stonefly nymph in Ferson Creek at the LeRoy Oakes Forest Preserve.
Talk about a reason to celebrate. Miss Pam was jubilant indeed! I tried, futilely, to contain my
glee as we examined the inch-long creature that we kept, briefly, in a white collection cup.
With more than 650 species in nine families in North America alone (3,400 species worldwide) I
wasn’t about to hazard a guess as to which group this individual belongs. But all the classic
stonefly hallmarks were there. Two tails, or cerci, two claws on each foot, and two sets of wing
pads, along with branched, filamentous gills poking out from beneath the thorax.
Later on, looking at the pictures we’d taken streamside, I thumbed through a few references
and was quickly reminded of how aquatic entomologists, to me anyway, seem slightly
masochistic. So many species, so many tiny parts…
Paging through options I decided that, if I had to make a guess, the Ferson Creek stonefly may
be a member of the Perlidae, a family also known as the common or summer stoneflies. Since I
savor my sanity, on a holiday weekend no less, that’s how far that i.d. will go. And even at that
it’s still a guess, a very tenuous one at that.
Regardless of identity, this little guy without a doubt belongs to a group of insects whose roots
date back to the Permian period, some 250 million years ago. Primitive in appearance (that is,
no showy swag like wing scales or hairs) stoneflies are strong climbers but weak fliers.
Populations are localized and tend to remain that way for eons.
While you won’t see stoneflies forming dense mating clusters the way various other River Bugs
do, these species have developed rituals that, I dare say, are even cooler: They drum.
Now, we’re not talking Buddy Rich or John Bonham-style percussion here. Stonefly drumming is
a subtle thing; it has to be. Even giant stoneflies, the largest North American species, measure a
scant 40 millimeters at maturity. If you’re not a stonefly, you’ll need special equipment to hear
the sound. But it’s drumming nonetheless, a behavior that, as one scientist puts it, “improves
the efficiency of mate-finding in an otherwise silent, drab, relatively sedentary insect.”
Male stoneflies are the ones that begin the performance, tapping their abdomens against a
surface, such as a log, in a species-specific pattern. Female stoneflies then indicate their
interest by drumming back in a simplified response pattern.
If all goes well, mating occurs, females deposit their eggs and the cycle begins again.
Fingers crossed, there will be lots of drumming along Ferson Creek this year. Stoneflies a few
years back were awarded the dubious status of “highly imperiled” by aquatic entomologists R.
Edward DeWalt, Colin Favret and Donald W. Webb of the Illinois Natural History Survey’s
Center for Biodiversity. Decades of habitat modifications, including dams, drain tiles, stream
channelization and development have made things tough for Illinois’ plecopterans.
Interestingly, the stretch of Ferson where the nature campers found their stonefly is just
downstream from a recent dam removal. Water now tumbles over boulders that had once
impeded the creek’s flow, creating a rush of clear, cool, well-oxygenated water.
I remember making a similar stonefly discovery in the Fox River at Glenwood Park Forest
Preserve, shortly after the south Batavia dam had been removed. This location, where aquatic
species diversity has measurably improved, is also a favorite hangout of another species once
considered imperiled—the bald eagle.
Stoneflies may not be as iconic as our nation’s symbol, but they’re no less important members
of our Fox River watershed. With continued attention to habitat improvement, including dam
modifications and stream re-meandering, there could come a day when stoneflies lose their
Holy Grail status.
Wouldn’t it be great if they were just another River Bug?
Pam Otto is the manager of nature programs and interpretive services at the Hickory Knolls
Discovery Center, a facility of the St. Charles Park District. She can be reached at 630-513-4346
or [email protected].