Swooping St. Croix swamps for swimming dragonflies | Science Museum of Minnesota

Field Notes
Field Notes

Swooping St. Croix swamps for swimming dragonflies

Tuesday, May 2, 2017
Posted by
Greg Seitz

Shadow darner nymph

The nymph (juvenile) form of a Shadow Darner dragonfly.

Dragonflies are insects that grow up in the water and spend a relatively short part of their life flying through the air in brilliant colors and with great agility. Humans are large primates different in almost every physical way, and bewitched by the beautiful bugs.

The people of the Minnesota Dragonfly Society are more enamored than average. They spend their free time exploring every possible kind of habitat, trying to discover what species live where in the land of 10,000 lakes, 6,500 streams, and 10 million acres of wetlands.

Their tools are waders and nets and enthusiasm.

Mitch Haag

Mitch Haag studies a specimen.

In 2015, I followed Mitch Haag, Curt Oien, and others through sphagnum moss, muddy peat, and knee-deep water in the Red Lake Wildlife Management Area while they searched for dragonflies. An article about the survey was published by the Minnesota Conservation Volunteer last summer.

Their passion, knowledge, and willingness to go almost anywhere immediately in pursuit of dragonflies captured my interest and my imagination.

On a gray Sunday in early April, I tagged along again on another Odonata adventure. This time, my five-year-old daughter joined me as we searched for rare species in a black-ash swamp at the Research Station’s Pine Needles Natural Area. The hunters included Mitch and Curt again, as well as Angela Isackson. All three have day jobs at Three Rivers Park District. Slogging through swamps is what they do on the weekend.

We were searching at Pine Needles because of the fourth hunter: Ron Lawrenz, founding director of the St. Croix Watershed Research Station, current director of Warner Nature Center, and dragonfly diehard. He thought the black ash swamp might host some unique species, and it had never been surveyed.

Curt Oien and Annika

Curt Oien (left) and Annika examine the fruits of his swooping.

Here, springs from the steep valley escarpment seep out of sandstone and through a flat forest of black ash, the ground soft with peat. Eventually the water trickles through the soft saturated soil of the swamp, accumulating in tiny creeks with sandy bottoms that spill down the final bedrock banks to the St. Croix River below.

The tall trees towering overhead and the cold spring water made it interesting to the dragonfly hunters. It would take a longer time than usual for the bugs to grow from nymph to adult, perhaps up to three years to hunt, eat, and transform.

These challenging conditions could mean uncommon species.

Shadow darner nymph.

Shadow darner nymph.

The seventeen-acre preserved area is best known as site of the Pine Needles cabin, where the Research Station hosts artists each summer to live and work on the banks of the river. Big, tall white pines populate the uplands where it’s drier.

The black-ash swamp has its own value, including as dragonfly habitat. There might even be Swamp Darners.

Swamp Darners (Epiaeschna heros) are one of the largest species of dragonflies in North America, reaching about three-and-a-half inches in length. Unlike most dragonflies, which love warmth and sun, they thrive in cool and shaded places. They have brilliant blue eyes, and a complex brown and green pattern on their body. Their wings are tinted amber.

Caddis fly

Another cool aquatic critter: a caddisfly larvae. 

There won’t be any adult dragonflies “on the wing” in such a cold season. But, because the insects spend most of their lives as nymphs, living underwater, researchers can find them all year by dragging rubber nets through streams and other shallow water.

Finding the nymphs is actually more helpful in some ways than finding the mature flying form. Adult dragonflies often travel great distances from their birthplace, but the presence of a nymph indicates that the site is breeding habitat for the species. Finding where they breed helps pinpoint the vegetation, water characteristics, or other factors affecting their reproduction.

And identifying breeding habitat is key to monitoring populations. Dragonflies are sensitive to changes in water quality and other environmental factors, so keeping an eye on them can reliably indicate when something goes amiss in the ecosystem.

The black mud and moss we were walking through was about seven inches deep. My daughter Annika’s boots were about six inches tall. But it didn’t matter when her purple pants got dirty. What mattered was the scientists, the dragonflies, the water.

The surveyors spread out through the swamp, searching for pools they could swoop, and we wandered between them. A stone’s throw from the St. Croix, the swamp is perched on sandstone banks near Marine on St. Croix. The big black ash trees have sprawling root systems above ground, a way for the roots to get oxygen in the decaying soil. The roots are woven into tangled webs of wood, looking a little like mangroves.

Ron told us that in a similar swamp farther up the St. Croix, at Sandrock Cliffs, biologists had taken core samples from ash trees and counted the rings. One tree was 400 years old, perhaps a seedling in 1610, pinpointed as a possible beginning of the Anthropocene, the “age of humans.” It was when Homo sapiens started to be the most significant force affecting the planet, mainly by moving species between East and West. American maize started growing in Europe, and wheat came to North America.

Transporting species from Europe to America also explains how people are poised to significantly affect the swamp at Pine Needles. Its ecology, including the dragonflies, is threatened by an invasive insect and shrub.

Humans helped the Emerald Ash Borer infest Minnesota when they transported firewood and other wood products bearing the insect larvae. It is expected to decimate Minnesota’s 1 billion ash trees in the years to come. Human-caused climate change is also making it easier for the borer to survive and thrive, as Minnesota gets fewer very cold winter days, which kill the larvae.

Arrowhead Spiketail

Arrowhead Spiketail nymph.

Buckthorn was brought to the area as a hedge plant, but quickly took over the understory in many types of forest. It is creeping into the swamp and threatening to disrupt the native vegetation and the waters. Read more about its impact in an upcoming Field Notes article.

The loss of ash and the invasion of buckthorn could significantly affect this swamp. Few other large trees will live in such wet, low-oxygen soil. When the ash are killed, it will likely have a ripple effect on many living things.

Seeing what species are here now could be very helpful in understanding how the ecosystem changes in the years ahead.

Curt Oien and Mitch Haag hunt dragonfly nymphs in a spring creek on the bluffs at Pine Needles.

Curt Oien and Mitch Haag hunt dragonfly nymphs in a spring creek on the bluffs at Pine Needles.

At first, the dragonfly hunters find the swamp water is choked with decaying leaves. The decomposition process is probably using up any available oxygen in the water, making the pools lifeless.

Annika and I take time to study the abundant skunk cabbage poking up. The plant is always one of the first living thing to show up in such swamps in spring. It gets a head start by generating its own internal heat, able to raise its core about 30-60 degrees Fahrenheit.

Skunk cabbage.

Then we hear Angela call out, “Got a darner.” We set off toward her, stepping over rotting logs and through cold puddles. My daughter is determined to get there without delay — not a typical characteristic. I’m worried that in her haste, she will stumble and fall into the mud. She doesn’t.

It’s not a Swamp Darner, but another unique shade-loving species, the Shadow Darner (Aeshna umbrosa). It is dropped into a Sweet Martha’s cookie bucket half-full of water. It might need to be studied under a microscope later to confirm its species. Or it might be raised in one of the researcher’s basements for this summer’s educational events. The researchers also find lots of scuds in their nets, the little freshwater shrimp that feed many fish and dragonflies. They also go into the bucket, where the darner nymph chases them.

We are on the peaty banks of the tiny creek that flows out of the swamp and toward the St. Croix. I can easily step across it. Annika can and does jump from one side to the other. Repeatedly.

The nets come up successful again, with a relatively huge nymph crawling around Curt’s palm, perhaps two inches long and looking armored for battle. This one is a spiketail, one of the two species found in Minnesota. It has a huge lower jaw, and it will bury itself in the sand on the bottom of such a creek with only its protruding eyes sticking up, and wait for prey to pass.

Later, Ron will look at it under the microscope, count some hairs and the proportional size of certain parts of the anatomy, and determined it is an Arrowhead Spiketail (Cordulegaster obliqua), an exciting find. It’s the largest member of the spiketail family.

The Research Station has been involved in dragonfly research since Ron was the director, more than twenty years ago. That’s when William Smith, a Wisconsin scientist, stayed at the station while he searched for specimens of what would be a new species found in the St. Croix River. The search for the St. Croix Snaketail was the subject of a 1997 article in the New York Times. Ophiogomphus susbehcha is named after the Lakota Sioux word for dragonfly, honoring the humans who had lived here as the insect’s neighbor for centuries.

Left to right: Curt Oien, Mitch Haag, Ron Lawrenz

The Arrowhead Spiketail and Shadow Darner were the only finds at Pine Needles. No Swamp Darners, even though one had been found in similar habitat last summer just upriver and on the other side of the St. Croix at Interstate Park in Wisconsin.

It was time for Annika and me to head home, so we split off from the crew as everyone left Pine Needles. The rest of the group went to check out a creek at Warner Nature Center. There, they found a species that had never been documented in Washington County, a Cyrano Darner. (The creature has a pronounced face, and is named after 17th-century French writer Cyrano de Bergerac’s famously big nose.)

In the months ahead, the hunters and the Minnesota Dragonfly Society will perform numerous surveys and public events, including at the Science Museum's Citizen Science Festival on May 20. Warner Nature Center will host a Dragonfly BioBlitz for any interested citizen scientist on Saturday, June 10. Mitch and Curt will look for Extra-Striped Snaketails (Ophiogomphus anomalus) in the headwaters of the St. Louis River system. The society’s annual gathering at Tettegouche State Park in July will offer opportunities for beginners and families, with the possibility of seeing Emeralds, a beautiful and rare family of dragonflies.

And everyone will keep wondering what’s living in just about every puddle in the state.