Highlighting Biodiversity: Searching for Snails in the Delaware River

As the Academy celebrates biodiversity — the remarkable, beautiful tapestry of life on Earth — this year, we are delving into some of the fascinating locations our scientists have visited in the region and across the globe to study and help protect our planet’s phenomenally diverse and incredible species. 

The Delaware River 

Free-flowing for nearly 300 miles across four states — New York, Pennsylvania, Delaware and New Jersey — the massive Delaware River is the lifeblood of the Northeast, providing not only drinking water for over 15 million people, but also critical freshwater habitat for countless aquatic and riparian wildlife species. 

There are over 200 tributary streams and creeks comprising an estimated 14,057 miles of sheer waterway in the Delaware River watershed. Each one of these creeks and streams is connected to the river and nearby land, both through their shared waters as well as with their shared ecosystems. Human actions in one creek can impact another stream; native and invasive species can be carried upstream or down. In other words, the health of the whole system is reliant on the care and understanding of its many parts and players.  

As the watershed lands surrounding this river are still about half forested (with 18% agricultural and 14% developed), benchmarking the diversity found here is crucial to creating a holistic picture of the health of this most important waterway — for the present and for the future. 

The Snails 

One of those critical species is the very small but mighty snail. Freshwater snails are a relatively understudied component of most waterways, including the Delaware River ecosystem. Compared to many other living groups in the Delaware River — birds, fish, plants, mammals— freshwater snails have received little scientific attention; few studies have included snails as a major focus, or if they do, rarely identify them to species level.  

H. anceps, ventral. Emma Guelzow/ANS

Thanks to their abundance and trophic level (feeding habits and role as prey), snails play an oversized but not fully understood role in the community and habitat structure of waterways. We know they contribute greatly to the nutrient cycling of the system by feeding on algae and muck at the bottom of the river, helping to clean the water. The snails then happily reproduce, providing a stable food source for others.  

Snails also function as a gauge to the overall health of the waterway. If the pollution levels are low, many different sensitive species can be found, creating a balanced and biodiverse habitat. If the waters or nearby land are not healthy, however, those species that are more tolerant of pollution will populate and take over — with rippling effects all the way up the food chain. 

At work collecting snails on the Upper Delaware Scenic and Recreational River. Tanya Dapkey/ANS

The Study 

Andy Weber, an ecologist at the National Park Service developed a study to assess the freshwater snail populations in the Upper Delaware Scenic and Recreational River, a northern portion of the river that is ecologically and economically valuable, as it features both cold and warm waters. To carry out the study, he turned to Emma Guelzow, a recent Drexel graduate from the Biodiversity, Earth and Enivronmental Science master’s program, and Tanya Dapkey, staff scientist at the Academy, both researching freshwater macroinvertebrates.  

Canoeing to their locations, these researchers explored 30 sites all along this area of the Delaware River to assess the freshwater snail populations found there. After the whole field crew, consisting of both ANS and NPS staff members led by Dapkey and Weber, used kick nets or catch-per-unit efforts to collect in the waters and along the river’s edge, Guelzow would then count and identify the snails — including the plants where they might have been located.  

B. subglobosa. Emma Guelzow/ANS

Back at the lab, ANS scientists and co-ops will inventory every single snail, down to its species level — work that requires careful patience, as many of these invertebrates are no bigger than a grain of sand. In one jar alone, they have counted over 300 snails!  

“We’re creating a snapshot in time,” Dapkey says of the study, aligning their collection points to coincide with eDNAtlas sites along the Delaware River. “In order to create a clear picture of biodiversity, we need a foundation. We have to first understand what is here and how well it is doing, to then know how to move forward in the best way.”  

Out of the estimated 60 native species of snails that are thought to occur in this area of the river, the scientists have identified 22 of them so far, a good sign of healthy waters. Unfortunately, they have also discovered some unwanted, invasive species lurking under the surface — the Chinese or Japanese mystery snails.  

“It is very difficult to tell these two mystery snails apart,” explains Guelzow, who is using cutting-edge, reliable genetic eDNA testing to properly determine which species they have collected. This crucial data will then help ensure that organizations can better direct their funding and conservation efforts. “Unlike the native species, they are not hard to spot; they are huge. We could see them by the water’s edge just looking down.” She says that these mystery snails were more often found at disturbed locations, such as boat launches or near human development.  

These large invasive species of snail are pollutant tolerant and can travel far in warm waters, making them a force to be reckoned with in the river’s ecosystem. Having this kind of competition alongside smaller, more sensitive species easily creates imbalance and food scarcity issues. They are also known to be hosts for parasites that impact fish and waterfowl.

And while it is possible these mystery snails might help clean the water or be a food source for larger organisms, the question this study asks is: at what cost?  

C. decisum. Emma Guelzow/ANS

The Future of the Region’s Biodiversity  

The scientific view of how rivers affect biodiversity, and vice versa, is constantly changing. Environmental impacts, such as storms, can certainly change their flow or movement. But rivers also endure many human-influenced impacts, too, such as erratically fluctuating changes in climate, infrastructure alterations around farms, dams and bridges or introduced invasive species. 

All things are connected in the environment. And as all these elements contribute to the state of our waterways — with even the smallest organisms like snails playing an essential role — gathering genetic data, identifying species and collecting specimens is critical now more than ever in constructing the story of biodiversity in the Delaware River. 

Director of the Pactrick Center for Environmental Research enjoying the scenery. Tanya Dapkey/ANS

Understanding, appreciating and conserving biodiversity has been at the core of the Academy’s science work since its founding in 1812. With 19 million specimens and counting, our collections are not only a window into the past, but also a critical tool for measuring the current and future health of all Earth’s species.  

During Biodiversity Year, join us as we bring our understanding of the natural world from the lab to City Hall and beyond, so that together, we are a force for nature. 


  1. Wow! Super informative and thankful to the Drexel team for doing this important work.
    Great images-I hope to share with my sixth grade students, who are studying macro invertebrates and their tolerance levels.

  2. A very good writing work. Excellent and fascinating information has been shared by you. I’ll keep reading your feedback and responding to it in the future.

  3. Very good article; it provided me with a lot of useful knowledge. As a blog, please continue to share more. I’ve added it to my bookmarks so that I can keep up with you.

  4. So honored to be able to say I was part of the field work team. It was great reading a small update on the work of Drexel and NPS. Working with this team was my favorite part of my internship with UPDE NPS. Can’t wait to read the final paper in the research.

  5. The Delaware River “Basin” is Absolutely Magnificent in so many places, and You can Order a “River Map” of any River in the United States, or it’s Territories from a USGS on it’s Website. These “River Maps” are of the “River” (a Free Flowing, Non Tidal body of Fresh Water) itself that are Printed on Plasticized Fold Out Sheets of Paper, with a “Date” on the Set.
    Don’t Forget that River’s “Evolve” every Year, because of erosion, which means that these USGS River Maps are Out of Date pretty quickly.
    The Delaware “River” itself on My Old USGS Map is actually 199.8 Miles Long from it’s Deepest Spot, which is a “Scour Hole” in the Catskill Mountains, in Hancock, New York to Trenton Falls, between Trenton, NJ and Morrisville, PA which is where the “River” Part of the Delaware River Basin actually Ends!
    The “Trenton Makes the World Takes” Bridge over the End of Trenton Falls was Built in 1895 by Trenton Bridge, using Steel I Beams and other Steel Parts from the US Steel Mill in Fairless Hills, PA, which Incidentally Finally Closed in 1998!
    The Scour Hole (Lake) in Hancock, New York is Formed by a Waterfall where the Northern Delaware River Drops into the Western Delaware River, from the North, which is Why it’s actually a Beautiful Lake, that on My USGS River Map was 191′ Deep.
    I Certainly am Not going to Pull Out My USGS River Map of the Delaware River, but I’m Pretty Sure it’s a 2000 Map?
    Incidentally, the US Highway 1 Bridge over the Delaware River Estuary wasn’t Completed until 1955, and it’s Over the Delaware River Estuary right next to the Trenton Makes the World Takes Bridge from 1895, and Trenton Bridge Corporation was Still Open and Was the Main Contractor for that Bridge too!
    Of Course You can Also Order River (Tidal) Estuary Maps for any River Estuary in the United States or Our Territories from the USGS too, and “My Sawbuck Says” that depending on Where Delaware Bay ends and the Atlantic Ocean Starts between New Jersey and Delaware, it’s Probably More than 100 Miles of Tidal Estuary?

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