Invasives from Beyond: Attack of the Mussels

U.S. Fish and Wildlife Service
8 min readOct 20, 2021

From slasher shlock to true crime benders, there is something for almost everyone to satisfy the insatiable appetite for the macabre. This obsession with serial killers, ghosts, and chainsaw-wielding psychopaths may not be something we all share, but at a minimum, even the most horror-adverse among us at least know who the big baddies are.

An animated GIF showing a black and white clip of Frankenstein’s monster turning his head.
Frankenstein’s Monster. Giphy.

For those who do like horror stories, here’s a stat that will scare even the most fearless among us: invasive species threaten nearly half of the imperiled species in the United States and have contributed to more than 40% of the current listings under the Endangered Species Act. Globally, invasive species are a primary cause of biodiversity loss, displacing native species and transforming ecosystems.

Unfortunately, invasive species can be found everywhere — on the ground, in the air, in our water… they could even be in your own back yard…

Horror villain Michael Myers relaxes in a hammock on a fall day
Michael Myers. Pinterest.

Throughout spring, we observe National Invasive Species Awareness Week and Invasive Plant Pest and Disease Awareness Month (April), putting the spotlight on some of the most notorious invaders, and so there’s no better time to talk about one of the scariest, most fiendish creatures spreading through North America with the relentless tenacity of The Blob:


Harry Potter characters screaming. Ron Weasley screams and throws down his Halloween treats, Neville Longbottom screams, and Draco Malfoy gets up from the table, screaming.
Dustin from the Netflix show Stranger Things screams and sprays hairspray at something off camera.
Left: Harry Potter and the Sorcerer’s Stone (2001). Tenor. Right: Dustin, Stranger Things Season 3 (2019). Giphy.

Zebra mussels and quagga mussels are very small freshwater mollusks that are invasive to North America (and many other places around the world). They are both named after the zebra-striped patterns on their shells, although it can be hard to see — they’re about the size of a fingernail.

(For the triviaphiles out there, put this in your back pocket: Quagga mussels are named after the “quagga,” an extinct relative of the zebra. The more you know!)

Eight adult zebra mussels are shown in comparison to the size of a penny. All eight mussels together are roughly the same size as the penny.
Photo by Sam Stukel, USFWS. Courtesy of South Dakota Game, Fish and Parks.

Zebra and quagga mussels are native to the Aral, Azov, Black, and Caspian seas of eastern Europe and western Asia. This dastardly duo was first introduced to several European freshwater ports in the late 1700s and first appeared in the Great Lakes area in the late 1980s.

Zebra mussels cover the entire top half of a red rock.
Photo by Schaeppi, National Park Service

Over the last 40 years (no, 1980 was not 20 years ago), zebra and quagga mussels have spread rapidly throughout the United States and can be found in freshwater rivers, lakes, reservoirs, and brackish water habitats. These sneaky little hitchhikers can move from place to place by attaching to boat hulls, anchors, trailers, and fishing equipment, and the larvae can actually get into water tanks and cargo holds.

A map of the continental US, showing the range of zebra and quagga mussels. Red dots across the eastern US indicate the spread of zebra mussels, the most dense areas in the Great Lakes & Midwest. Green dots in the Great Lakes region & southwest US show the spread of quagga mussels. Yellow dots in the Great Lakes region and sporadically in the western U.S. show where both invasive mussels have been identified. Purple squares show a few successful eradication efforts along the east coast & Texas
Zebra and Quagga Mussel Sightings Distribution (2021). Map produced by the U.S. Geological Survey.

Small but Mighty

A pile of larval quagga mussels
an animated GIF of the Mogwai known as Gizmo in the movie Gremlins 2, looking adorable.
Sure, they look cute, but have you seen Gremlins? Mogwai can bat those eyes like the best of us, but don’t fall for it — invasive mussels are as disastrous as gremlins on a rampage! Left: Photo courtesy of South Dakota Game, Fish and Parks. Right: Gremlins 2 (1990). Giphy.

Although they may seem small and harmless, these teeny-tiny terrors can multiply at rates that rival a zombie apocalypse — a single female can produce up to 1 million eggs a year.

Hypothetically, if 10% of the offspring survived, there would be 10 septillion mussels in the waterway at the end of five years. That’s a lot of mussels.

an animated GIF of actor Zach Galifianakis thinking in the movie The Hangover. Superimposed over his face are complicated math equations.
Left: Math, The Hangover (2009). Giphy.

In some facilities in the Great Lakes area, zebra mussels have been reported in numbers over 700,000 individuals per square meter, and their capacity to cause damage is what you’d expect from a Stephen King story. These invasive mussels leave a wake of destruction wherever they go, impacting ecosystems, infrastructure, and local economies.

As filter feeders, these species remove large amounts of microscopic plants and animals that form the base of the food chain, leaving little or nothing for native aquatic species. They also attach to the shells of native mussels, turtles, and crustaceans, starve other filter feeders, and produce enough waste to change ecosystems and impair water quality, even going so far as to affect the taste and smell of drinking water.

The chaos doesn’t stop there, either. Zebra and quagga mussels attach to most underwater structures and can form dense clusters that clog water pipes, filters, trash screens, canals, aqueducts, and even dams, all of which requires a lot of money to fix. Power plants, water treatment plants, and dams spend hundreds of millions of dollars in maintenance and cleanup efforts every year, with costs already surpassing several billion dollars.

And there’s more: these mussels can overtake and cause damage to boat ramps and docks, foul beaches, destroy boat engines and cooling systems, and can even sink navigational buoys, breakwaters, docks, and small vessels.

a population of zebra mussels completely cover a boat propeller. Only small parts of the propeller are visible under the mussels.
a population of invasive mussels cover the side of a shopping cart.
Left: Zebra mussels on a boat propeller. Photo by Sam Stukel, USFWS. Right: Photo courtesy of South Dakota Game, Fish and Parks.

And before you ask, no you can’t eat them. In fact, they’re about as difficult to kill as Michael Myers. Once these foul filter feeders become established in a water body, there are no species-specific control methods that can be used to eradicate the population without causing harm to the natural environment. So far, there have been only two accounts of successfully eradicating zebra mussels, and one was an isolated 12-acre quarry in Virginia. The second case was in Lake Waco, Texas, where early detection of zebra mussels prompted a multi-agency rapid response effort that was able to stop the invasion before it was too late.

Eradicating or treating zebra or quagga mussels in large water bodies or connected waterways may not be possible, so prevention is very important — follow the three-step Clean, Drain, Dry process to prevent spreading invasive mussels!

But Wait! Not All Mussels Are Monsters!

An animated GIF showing a black and white clip of Frankenstein’s monster reaching out and looking around. The word “Friend” appears on the bottom.
Frankenstein’s monster just wants a friend. Tenor.

While quagga and zebra mussels wreak havoc on ecosystems, native freshwater mussels are actually known fondly among water-loving biologists as “the liver of the river” because of their critical role in filtering water. Mussels are natural filters, purifying aquatic systems by feeding on algae, plankton, and silts — and they can even filter out E. Coli! A single freshwater mussel is estimated to filter eight gallons of water per day.

To put it in perspective, that’s like drinking 32 Nalgene bottles of water every day.

Jimmy Fallon falls over as he attempts to drink out of a 5-gallon water cooler jug.
Thirsty Jimmy Fallon. Tenor.

The very presence of diverse, native freshwater mussels is an indicator of a healthy ecosystem with good water quality. Unfortunately, native mussel populations have seen a drastic decline in recent decades due to invasive species, disease, pollutants, sediment, habitat loss, and changes to water flow and temperature caused by infrastructure. In fact, freshwater mussels are the most imperiled group of animals in North America, with 66% of species at risk, which is particularly sobering when considering that these stats are closer to 16% for mammals and 15% for birds.

Sediment and other debris can smother native mussels, while pollutants such as pesticides, fertilizer, herbicides, mercury, and lead can poison mussels, leading to gastrointestinal and neurological trauma. Disease is also a major cause of mussel mortality. Scientists with the U.S. Fish and Wildlife Service, U.S. Geological Survey, and the University of Wisconsin-Madison have discovered a virus that causes lethal epidemic disease and increased mass mortality among invertebrates and mussels.

Across the country, scientists and land managers are using the best-available science and management practices, including captive breeding and restocking efforts, to protect and restore these critical and imperiled species. Biologists in South Dakota and Wisconsin are working on an experimental mussel project to restore black sandshell mussel populations. In North Carolina, Appalachian elktoe mussels were restocked in the French Broad River, followed a few years later by wavy-rayed lampmussels, which had been missing from the river for a hundred years.

A hand reaches into a bag of small mussels.
Bag of golden riffleshell mussels. Photo by Gary Peeples, USFWS.

Golden riffleshell mussels were also released into Virginia’s Clinch River and Indian Creek, 20 years after a chemical spill eliminated the mussel from the Clinch River.

Laws such as the Endangered Species Act and Clean Water Act are contributing to recovery efforts, but more needs to be done to save many of these species from extinction.

How Can You Help?

Enter the hero of our story. How can one aspire to be the Sidney Prescott, Van Helsing, Ash Williams, or Lorie Strode of this terrible tale? Just like our favorite horror icons, anyone can be the hero of their own story — just, maybe, don’t be the first one to investigate that mysterious sound in the basement.

We can all channel our inner hero and fight back against these invasive-mussel-monsters, while also doing out part to protect those that can’t defend themselves.

An animated GIF of characters Ash Williams, Pablo Simon Bolivar, Kelly Maxwel, and Ruby Knowby standing together in the show Ash versus the Evil Dead. The words “Let’s go save the world” appear at the bottom.
Ash Versus the Evil Dead (2016). Giphy.

How you can help:

  • Limit or cease pesticide use to conserve soil and prevent runoff into nearby lakes and streams.
  • Help control soil erosion by planting trees and plants to avoid runoff of soil into freshwater areas.
  • Clean, drain, dry! Remove aquatic weeds from boat trailers and motors again to prevent the spread of invasive mussels. Don’t throw weeds back into the water!
  • Support and follow invasive mussel quarantine, inspection, and decontamination programs.
  • Inspect aquatic store purchases like moss balls! In 2021, zebra mussels were found in moss balls sold at aquarium and pet supply stores, garden centers, florist shops, and online retailers. Live mussels from moss balls could be released into a storm drain or flushed into a waterway and cause significant damage. Destroy, dispose, drain!
  • Report sightings of invasive mussels and other non-indigenous aquatic species with the USGS sighting report form.
  • Share what you know!
A shot of actor Jesse Eisenberg in the movie Zombieland. Next to Jesse’s face are the words “Rule #17 Be a Hero”
Be a hero! Zombieland (2009). Tenor.

Written by Christina Stone, a Public Affairs Specialist in Lakewood, Colorado, in collaboration with Mindy Meade, Jessica Sutt, Gabie Wolf-Gonzalez, Roya Mogadam, Donna Allard, Jennifer Poirier, Tom MacKenzie, David Britton, Kim Mitchell, and Rob Stone.



U.S. Fish and Wildlife Service

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