Biologist McNair to Present BTG Brown Bag on Dragonflies, Restoration of Wetland Habitat

There’s a moment in “The Matrix” when Keanu Reeves realizes his life is a simulation and physics don’t apply. Everything moves in slow motion, and he impossibly dodges punches, anticipating the attacks of Agent Smith in an exhausting display of martial arts.

For real-life dragonflies, that’s a normal day.

“A dragonfly’s flicker fusion is so rapid that basically everything to it looks like slow motion,” said Dennis McNair, emeritus biology professor at the University of Pittsburgh at Johnstown.

Flicker fusion refers to how an organism’s eyes perceive motion. Film moving at 24 frames per second creates the illusion of motion for humans. Dragonflies, on the other hand, have greater flicker fusion that allows them to perceive motion with much more detail, hence the relative slow motion.

Great eyesight is what allows dragonflies to catch fast-moving prey ranging from bees to horse flies to even hummingbirds, according to McNair, who’s spent two decades researching the insects.

He’ll deliver a Brown Bag lecture at 12:15 p.m. Tuesday in Smith Wilkes Hall to discuss the restoration of wetlands in Bedford County, Pennsylvania, where he monitors dragonfly and damselfly populations.

Different species take different forms, but many adult dragonflies feature iridescent wings and dazzling eyes that encourage countless nicknames. McNair said some refer to larger dragonflies as “darning needles” due to the motion of their slender abdomens.

“When you see them flying along over the surface of the water and dipping their back end regularly in the water, it looks like they’re perhaps a needle sewing a stitch across the water,” he said. “My grandmother used to say if I told a lie, they’d come along and darn my mouth shut.”

Adult damselflies resemble dragonflies, but slender abdomens, more like a sewing needle, replace the dragonfly’s muscular torsos. Damselflies fly in a gentler, fluttering motion, whereas McNair said dragonflies are fast fliers, with more “robust” motion.

Those adults zip about, typically eating hundreds of mosquitoes and other insects per day. Their front legs form a basket to capture prey, and strong mandibles chew it to bits. Dragonflies in Chautauqua, McNair said, are particularly visible along the shoreline at dusk, when the mosquitoes are most active.

Compared with the elegant adults, dragonfly and damselfly larvae are ugly, aggressive ducklings. The larvae are aquatic, swimming through shallow lake water. McNair described the feeding process of dragonfly larvae, whereby an arm located beneath the mouth extends to grab prey and shovel it into the mouth above. That arm ensnares other insects and even small fish with such efficiency that McNair said they’re a dreaded nuisance for local fish hatcheries.

McNair is part of a team that purchased and restored 120 acres of wetland in Pennsylvania that was once corn fields. For 20 years, he has monitored the return of native plants and species, including dragonflies.

Research like McNair’s is still in its infancy, he said, and biologists continue to establish a baseline for dragonfly and butterfly populations nationwide. But, even at that early stage, McNair said the insects reveal themselves as valuable indicators of environmental quality. By looking at dragonflies and damselflies, he said biologists can get a read on the health of the ecosystem and even larger phenomena, such as climate change, which can extend or limit a species’ range.

But those indicators are only useful where they can find habitat. On that note, McNair has one piece of advice regarding wetlands such as the one he monitors in Bedford County: “Leave them as they were.”

Morgan Kinney

The author Morgan Kinney

Morgan Kinney is a Northwestern University journalism student who likes to explain things, particularly science. Read his Twitter thoughts @morgan_kinney.