Originally published on June 15, 2021
This story is part of our series, Wild Pennsylvania. Check out all of the other stories in the series here.
Ryan Utz says his recent paper on dragonflies, published in the journal American Midland Naturalist, came about as a result of a happy accident.
“We turned up some data that we weren’t intending to find, and then found something pretty cool,” Utz, assistant professor of water resources at Chatham University, said.
The data were dozens of specimens of dragonfly and damselfly larvae, of the order Odonata. The samples were taken from the Ohio River, not far from the Point, where Pittsburgh’s three rivers meet.
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Utz said colleagues from Duquesne University and others saved the samples from routine biomonitoring efforts on the river in 2014 and 2019. The dragonfly larvae were trawled from the bottom of the river, along with organic material, as the scientists were sampling for fish.
The larvae were preserved and studied in a lab. The conservation status of the 6 dragonfly and one damselfly species found were determined through the public database tool, NatureServe Explorer.
Researchers found:
- All of the dragonfly species found in the samples were of conservation concern somewhere in the US.
- Only one damselfly species, dusky dancer (Argia translata) was found. Researchers suspect the holes in the trawling nets could have been too large to capture the smaller damselflies in the river.
- There were almost as many samples of dragonfly larvae taken from the deeper parts of the river as there were from near the banks of the river, in more shallow water, where scientists expected to find the majority of samples because of food and habitat resources.
Ian Hart, an undergraduate in Chatham’s environmental science program, said the elusive clubtail (Stylurus notatus) was the most abundant species found among the larval specimens. Its conservation status is vulnerable in Pennsylvania but imperiled in the other Ohio River states of West Virginia, Kentucky and Indiana.
“It gets its name because as an adult, it spends much of its life high in forest canopies,” Hart said. “It makes it really hard for us humans to actually study them because they’re just always kind of out of our reach.”
Hart, who is actually the first author on the published paper, said the abundance of the species in the specimens could mean it is just easier to study and catalog in its larval state, and may not be as imperiled as researchers had thought.
Dragonflies live underwater in their larval stage, sometimes up to a couple of years, until they are ready to metamorphose into an adult. They are predators, hunting other insects, and even fish.
Biodiversity in the Ohio
Utz said it was surprising and encouraging to discover species of dragonflies of conservation concern in an industrial river like the Ohio.
“The sheer number of dams and locks upstream means that the way the river behaves is radically changed, and the changes make it behave a lot more like a lake,” he said.
Utz said you might not expect to see the species of river-dwelling organisms, like the odonata they found, in this ecosystem anymore because the Ohio River doesn’t act like a river anymore. The many industrial uses of the river also create disturbances and pollution for aquatic insects.
“While the Ohio River is very changed from what it once was, the fact that we found at least some diversity of Odonata in the Ohio River, including species that are supposed to be river dwellers, is somewhat good news for the Ohio,” he said.
Utz says aquatic insects are indicators of the health of an ecosystem, but there hasn’t been a lot of research into dragonflies in the Ohio. Utz says other aquatic insects, like a species of mayfly and a giant stonefly, were also among the specimens, and he wouldn’t expect to find them in this habitat.
“Our freshwater ecosystems are very important,” Ian Hart said. “We don’t know what it was like before human impacts as early as the 1800s or before. There’s definitely a need to continue to study these important environments and learn more about them.”
