Creature Feature: The rare dragonfly that bears the St. Croix River’s name

St. Croix Snaketails have only been known to exist since 1989, when researchers stumbled on the species on the upper river.

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Ophiogomphus susbehcha (St. Croix Snaketail), collected in 1991 at Sand Rock Cliffs on the St. Croix River. (Photo courtesy Smithsonian National Museum of Natural History)

On June 18, 1989, scientists working for the Wisconsin Department of Natural Resources made a fascinating find on the upper St. Croix River, at County O Landing north of St. Croix Falls. It took years afterwards, but they eventually confirmed the discovery of a new species of dragonfly, never before known to science.

Dragonflies are amazing creatures known for aerial acrobatics. The St. Croix River is home to abundant and diverse dragonflies — they lay eggs and grow to maturity in the river, requiring clean water and a rich ecosystem, and then emerge into the air above, spending their final few months of life feasting on flying insects and producing the next generation.

The scientists were collecting exoskeletons left behind by molting dragonflies, using them to determine what species were present in the area. Dragonflies are born and grow over a period of months and years in water — and when they crawl out and transform into their flying stage of life, they leave behind “exuvia.” The species can often be identified based just on these “husks.”

Because they are airborne for only a small portion of their lives, and may not be visible on cool or cloudy days, and may hang out in inaccessible locations as adults, surveying the population via exuvia is essential.

Discover and confirm

County O Landing. (Greg Seitz, St. Croix 360)

On that summer day 31 years ago, biologist William Smith found 16 exuvia that looked different than any he had seen before, and he couldn’t match them to any other known species. Back in his laboratory in Madison, he confirmed features that distinguished it from related species in the clubtail family.

That November, he went back to the St. Croix. In water a few feet deep, where the current was so powerful that the wading scientists had “extreme difficulty remaining in place,” he found living larvae that matched the exuvia.

Smith took them back to his lab and raised them in an aquarium until they metamorphosed into adults. Sure enough, they were a species new to science. The New York Times wrote about the discovery a few years later.

“‘In the continental United States, finding a new species is not an everyday occurrence,” Smith told the newspaper. “Most workers in the field — there are maybe two in each state — have not described a new species. But in the last few years there’s been an upsurge in interest in dragonflies, and when you begin to look very carefully, new species show up.”

The next summer, he went back to the site and found adults flying around. Over two days in late May, 1990, Smith observed a mass emergence of hundreds of St. Croix Snaketails crawling out of the river and flying away. They seemed to head for nearby open areas, where they feasted on flies.

St. Croix Snaketail adults are also believed to spend a lot of time in the forest canopy, where they are mostly out of sight and out of reach for scientists.

A creature of clean water

Title page of 1993 paper that first described the St. Croix Snaketail.

Smith collected hundreds of exuvia and fresh adult specimens, and set to work carefully documenting the species. In 1993, he and and a colleague, Timothy Vogt, published a paper describing the St. Croix Snaketail for the first time, adding it to the list of what’s now 326 species of dragonflies found in North America.

They dubbed it the St. Croix Snaketail, or Ophiogomphus susbehcha. (Ophiogomphus is the genus for clubtail and susbehcha is the Lakota Sioux word for dragonfly.) Snaketails are a group of of dragonflies with bulges at the end of their tail, resembling the head of a serpent.

In their paper, the two scientists describe the species in highly specific, technical language. Each tiny part of its body is accounted for, with size and color, often explaining the proportional size comparing different parts of the insect. Here’s a sample:

“Tergum 1 yellow dorsally, dark brown dorsolaterally, gray laterally. Tergum 2 dark brown with middorsal longitudinal yellow marking extending posteriorly to posterior transverse carina, marking constricted at supplementary transverse carina and posterior 1/3; auricles green with black tubercles posteriorly; small brown marking posterior to each auricle; large ventral gray marking anterior to posterior transverse carina.”

This type of language is necessary for accurate science, but foreign to most folks. In less technical terms, the St. Croix Snaketail is fairly large, at about two inches long, and primarily black, green, and yellow. It has unique genitals, and a big backside characteristic of its clubtail cousins.

The scientists reported finding the species at 11 total sites along the St. Croix River, mostly on the upper river, and also at Interstate Park. It was also found at two sites on the Chippewa River, east of the St. Croix.

“Larvae are known only from medium-sized, fast-flowing rivers with pristine water quality,” the paper reported. They are found in places where the river bottom is sand, gravel, and rock.

Since then, despite extensive searches of more than 180 streams in the region, the species has been found only in a few other places, including the Potomac River in Maryland in 2002 and the James River in Virginia in 2006. (A Richmond, Va. craft brewery even created a “Snaketail Ale” in its honor in 2016.)

Almost lost before it was found

A St. Croix Snaketail observed in Virginia. (Kathy Richardson, iNaturalist)

The fact that there are populations spread so far apart hints at why they are so rare today.

America used to have many clean, mid-sized, free-flowing rivers, but many were degraded by dams, pollution, and other forces. The rivers the St. Croix Snaketail needs to breed are the same ones that have been heavily used and abused by industry and hydropower. The large gap between Wisconsin and the East Coast indicates they were probably found throughout the eastern United States before much of their habitat was destroyed.

The St. Croix River is one of the few remaining rivers that have been protected and remained suitable for the species. This summer, several people reported observing St. Croix Snaketails on iNaturalist, across its range.

A 1999 report by the Minnesota Department of Natural Resources (co-authored by William Smith) stated that no St. Croix Snaketails had bee found above Norway Point on the upper river, and none were found below Marine on St. Croix. The highest density was between the Snake River south to Never’s Dam.

Today, St. Croix Snaketails are listed as endangered in Wisconsin and threatened in Minnesota. Their populations are small and isolated, and could easily be wiped out.

“The immediate river corridor is well protected by the National Park Service,” stated a 1999 report from Tributaries with watersheds outside of the protective corridor are probably the biggest threat to log-term survival of the St. Croix biota. The Snake R was noted to be running very muddy after a rainfall event in contrast to the St. Croix. Nonpoint pollution control on the Snake should be a priority of the MN DNR

Nonetheless, each May and June, they continue to crawl out of the St. Croix River and continue their life cycle. Dragonflies have been around for hundreds of millions of years, surviving huge global changes.

There are new challenges to the St. Croix Snaketail’s survival since its discovery. There are 80 million more people in America. Rollbacks of environmental laws have weakened protections. The St. Croix is protected by state and federal legislation, but its watershed is not. This delicate creature has endured a lot already, and the question now is how much more it can take.

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One response to “Creature Feature: The rare dragonfly that bears the St. Croix River’s name”

  1. Ted Eastlund Avatar
    Ted Eastlund

    Great article.

    We are the the first major watershed below the origin of the St Croix River.

    To preserve the critical habitat of the rare St Croix Snaketail dragonfly downstream, we need to keep our Eau Claire Lakes and the Eau Claire River clean and healthy,

    It is not easy with the high-speed waterski boats and the low-speed wake surfing wake boats causing shoreline erosion and disturbing lake bottom sediments and our constant battle with invasive aquatic plants.

    Ted Eastlund

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Creature Feature: The rare dragonfly that bears the St. Croix River’s name