It sounds like a movie title: Sleeping with the Enemy. But it’s also the strategy one of the rarest dragonflies on earth is using to survive.
Thought to be extinct since the 1950s, an adult Hine’s emerald dragonfly was discovered at The Nature Conservancy’s Mink River Preserve in Door County, Wisconsin, in 1987, by Bill Smith, a zoologist with the Wisconsin Department of Natural Resources.
Now, the Conservancy is protecting groundwater recharge areas important to the dragonfly’s larvae, which may be the key to the species’ survival.
Prior to the dragonfly’s rediscovery, little was known about the 2.5-inch-long insect. But Dr. Dan Soluk, associate professor of biology at the University of South Dakota, is changing that. Soluk and his students have spent almost 16 years studying Hine’s emerald dragonflies in Wisconsin and Illinois.
For most of that time, they have been based at a Conservancy cabin at Mink River, giving them regular access to Hine’s emeralds from April to October. But finding a species that spends only a few weeks of its life as a flying adult is a challenge.
“Our first big breakthrough came in 1997, when we discovered that Hine’s larvae were most abundant in intermittent streams,” said Soluk. They live in places where their habitat dries up.”
But how do the larvae survive during the dry spells? Soluk and his graduate student Lauren Pintor eventually figured out that Hine’s larvae use crayfish burrows. Devil crayfish can burrow more than two meters to maintain contact with the falling water table, making the burrows great places to hang out during dry periods and the winter months.
“It’s really the last place we looked,” Soluk commented. “They shouldn’t be there because crayfish eat dragonfly larvae. But they don’t eat all of them, so the benefits are obviously greater than the risk.”
“Hine’s emeralds live for three to five years, and they spend most of their lives as larvae,” said Soluk. “The larvae live in small streams fed by groundwater. So protecting the groundwater supply is critical to the survival of this animal.”
In 2008, the Conservancy, U.S. Fish and Wildlife Service, Door County Soil and Water Conservation Department and Wisconsin Department of Natural Resources partnered with the Wisconsin Geological and Natural History Survey to map the groundwater recharge areas in Door County important to the dragonfly larvae. Mink River estuary and several other wetlands were at the top of the list.
Today, the Conservancy protects critical habitat for the dragonfly at four Wisconsin preserves: North Bay-Mud Lake, Kangaroo Lake, Shivering Sands and, of course, Mink River.
Soluk says there’s still a lot we don’t know about the Hine’s emerald that could be important to its recovery and long-term survival. But, fortunately, he’s the curious type and continues his work to unlock the secrets of this rare and mysterious creature.
By Cate Harrington, Nature Conservancy senior conservation writer