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Quadrula nodulata

What do they look like?

The shell of the wartyback is thick. It is rounded at the front end, while its back end is squared. The color of the shell varies from yellowish green to light brown in small mussels, to greenish brown or dark brown in larger mussels. The average wartyback mussel is usually 3 to 4 inches (7.6 to 10.2 cm) in length. (Cummings and Mayer, 1992; Illinois Natural History Survey, 2013; Minnesota Department of Natural Resources, 2013)

  • Sexual Dimorphism
  • sexes alike
  • Range length
    7.6 to 10.2 cm
    2.99 to 4.02 in

Where do they live?

Quadrula nodulata, also known as the wartyback, is a species of freshwater mussel that lives in the United States. It is distributed throughout the entire Ohio, Cumberland, and Tennessee river systems, and the Mississippi River drainage from Wisconsin and Minnesota, south through Kansas and Oklahoma to Texas, and east to Louisiana and Mississippi through Ohio. (NatureServe, 2013; Williams, 2008)

What kind of habitat do they need?

The wartyback mussel lives in medium to large rivers and reservoirs that have a mud, sand, or gravel bottom. (Cummings and Mayer, 1992)

  • Aquatic Biomes
  • benthic
  • rivers and streams
  • Range depth
    5.5 (high) m
    18.04 (high) ft

How do they grow?

Male mussels release sperm into the water, which the water carries to females located downstream. When the sperm goes inside the female body, it fertilizes the eggs. The eggs stay in the gills of the female, and they hatch there into larvae called glochidia. The glochidia stay in the female for about a month. To continue development, glochidia need to attach to a fish host, where they will stay as parasites. The female parent releases the glochidia into the water so that they can attach to a host. They develop into juvenile mussels, and then drop off the fish into the mud or gravel on the bottom of the stream, where they develop into adults. Fish hosts for the glochidia of the wartyback include black crappie (Pomoxis nigromaculatus), white crappie (P. annularis), bluegill (Lepomis macrochirus), channel catfish (Ictalurus punctatus), and largemouth bass (Micropterus salmoides). (Parmalee and Bogan, 1998; Watters, 1994)

How do they reproduce?

To mate, wartyback males release their sperm into the water. This is called spawning. The sperm is carried downstream by the water to female mussels. The sperm enters the body of the female through a tube called the incurrent siphon. Spawning happens when the water temperature changes. (Parmalee and Bogan, 1998; Watters, 1994)

After the eggs are fertilized, they stay inside the gills of the female. The eggs also hatch there into glochidia. The glochidia stay in the gills for about a month, from June to July. The female then releases the glochidia into the water, where they attach to a fish and act as parasites. Wartybacks reproduce once a year. (Parmalee and Bogan, 1998; Watters, 1994)

  • How often does reproduction occur?
    Wartyback mussels breed once yearly.
  • Breeding season
    Reproduction takes place during June and July.
  • Average number of offspring
    several thousand

Female wartyback mussels provide care by keeping the eggs and the glochidia in their gills for about a month before releasing them into the water. Once the glochidia are released, they do not return to the mother and do not get any more parental care. (Parmalee and Bogan, 1998; Watters, 1994)

  • Parental Investment
  • pre-hatching/birth
    • provisioning
      • female

How long do they live?

It is not known how long wartyback mussels live, but other related mussel species live for several decades, with some living up to 100 years or more. (Sietman, 2003)

How do they behave?

The wartyback mussel spends most of its life buried in the mud at the bottom of rivers and streams. They often live in groups with many other mussel species, called mussel beds. Wartyback mussels mostly stay in the same place, but they can move if necessary. They use a muscle called the foot that they can stick out of their shell and use to push and pull themselves around. (Sietman, 2003)

How do they communicate with each other?

Mussels can perceive water temperature. It is likely that glochidia find fish hosts by detecting certain chemicals, but there is not much known about this. Wartybacks can also detect touch, light, and some chemicals. (Watters, 1995)

What do they eat?

Wartyback mussels feed on small particles of food and microorganisms in the water, such as bacteria, protozoans, and algae. They filter the particles out of the water. The water moves into their body through a tube called the incurrent siphon. The particles are removed from the water by their gills, and then the food is carried to the mouth by tiny hair-like projections called cilia. The leftover water leaves the body through another tube called the excurrent siphon.

Glochidia are parasites on fish. They feed on blood and nutrients from the fish. (Arey, 1921; Meglitsch and Schram, 1991; Sietman, 2003; Watters, 1995)

What eats them and how do they avoid being eaten?

Predators of wartyback mussels are muskrats, raccoons, American minks, North American river otters, and some birds. Juveniles are probably eaten by many freshwater fish, such as freshwater drum, lake sturgeon, spotted suckers, redhorses, and pumpkinseeds. The wartyback's shell can protect it from some predators, and burrowing in the mud on the river bottom also allows it to hide from predators. (Cummings and Mayer, 1992; Watters, 1995)

What roles do they have in the ecosystem?

Mussels filter particles out of the water, which can make the water clearer. They are also an important part of the food chain and are eaten by many mammals and fish. They can be infected by parasites, such as mites, trematode worms, and midge larvae that feed on their gills and other soft body parts. Wartyback mussel glochidia are parasites and attach to many species of freshwater fish to complete development. (Cummings and Mayer, 1992; Minnesota Department of Natural Resources, 2013; Watters, 1995)

Species (or larger taxonomic groups) used as hosts by this species
Commensal or parasitic species (or larger taxonomic groups) that use this species as a host

Do they cause problems?

Wartyback mussels do not cause any problems for humans.

How do they interact with us?

Mussels can be used by scientists to study the environment. Since mussels filter particles out of the water, if the water is polluted, they will collect pollution in their bodies. Scientists can study mussels and learn about their aquatic environment. The wartyback mussel, along with other freshwater mussel species, has been used to make pearls and buttons in the past. (Missouri Department of Conservation, 2013)

  • Ways that people benefit from these animals:
  • body parts are source of valuable material
  • research and education

Are they endangered?

Wartyback mussels are not an endangered species, but they are considered threatened in many states. This is because of habitat destruction, as people change their habitats with pollution and construction. Zebra mussels are an invasive species that can also cause problems for wartyback mussels. They take over the habitat, using resources, and also attach themselves onto the shells of other mussels, causing suffocation and death. Efforts need to be made to prevent wartyback mussels from becoming an endangered species, and people need to be careful about how their activities can change an environment and effect the animals in it. (Minnesota Department of Natural Resources, 2013; NatureServe, 2013)

Some more information...

The wartyback was previously recorded as Quadrula nodulata, but is now known as Amphinaias nodulata. (Graf and Cummings, 2007)


Eric Krumm (author), Minnesota State University, Mankato, Robert Sorensen (editor), Minnesota State University, Mankato, Angela Miner (editor), Animal Diversity Web Staff.


Arey, L. 1921. An experimental study on glochidia and the factors underlying encystment. Journal of Experimental Zoology, 33: 463-499.

Brusca, R., G. Brusca. 2003. Invertebrates. Sunderland, MA: Sinauer Associates Inc..

Cummings, K., C. Mayer. 1992. Field guide to freshwater mussels of the Midwest.. Champaign, Illinois: Illinois Natural History Survey.

Graf, D., K. Cummings. 2007. Review of the systematics and global diversity of freshwater mussel species (Bivalvia: Unionoida).. Journal of Molluscan Studies, 73: 291-314.

Illinois Natural History Survey, 2013. "Quadrula nodulata" (On-line). Accessed February 22, 2013 at

Meglitsch, P., F. Schram. 1991. Invertebrate Zoology. Oxford, England: Oxford University Press.

Minnesota Department of Natural Resources, 2013. "Species Profile of Quadrula nodulata (Wartyback)" (On-line). Accessed March 23, 2013 at

Missouri Department of Conservation, 2013. "Wartyback species profile" (On-line). Accessed March 25, 2013 at

NatureServe, 2013. "NatureServe Explorer" (On-line). Accessed March 20, 2013 at

Parmalee, P., A. Bogan. 1998. The freshwater mussels of Tennessee.. Knoxville, Tennessee: The University of Tennessee Press.

Sietman, B. 2003. Field guide to the freshwater mussels of Minnesota.. St. Paul, Minnesota: Minnesota Department of Natural Resources.

Watters, G. 1995. A field guide to the freshwater mussels of Ohio. Columbus, Ohio: Ohio Department of Natural Resources, Division of Wildlife.

Watters, G. 1994. An annotated bibliography of the reproduction and propagation of the Unionoidea (Primarily of North America).. Ohio Biological Survey Miscellaneous Contributions, No. 1, Columbus, Ohio: 158 pp.

Williams, J. 2008. Freshwater Mussels of Alabama & the Mobile Basin in Georgia, Mississippi & Tennessee.. Tuscaloosa, Alabama: University of Alabama Press.

University of Michigan Museum of ZoologyNational Science Foundation

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Krumm, E. 2014. "Quadrula nodulata" (On-line), Animal Diversity Web. Accessed May 23, 2024 at

BioKIDS is sponsored in part by the Interagency Education Research Initiative. It is a partnership of the University of Michigan School of Education, University of Michigan Museum of Zoology, and the Detroit Public Schools. This material is based upon work supported by the National Science Foundation under Grant DRL-0628151.
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