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Megalonaias nervosa

What do they look like?

Shells of the washboard are rectangular and covered with loops and folds, which makes the washboard look much different from other mussels. Young washboards are known to have fine ridges and folds. These ridges and folds become more noticeable as the mussel ages. The outer surface of the shell is black or brown. The inner surface of the shell is white and known as the nacre. ("Megalonaias nervosa", 2011; Haag, 2012; "Megalonaias nervosa", 2014)

  • Sexual Dimorphism
  • sexes alike
  • Range mass
    263.8 (high) g
    9.30 (high) oz
  • Range length
    40 to 250 mm
    1.57 to 9.84 in

Where do they live?

Megalonaias nervosa, a freshwater mussel called the washboard, can be found in 18 states around the United States. It is found from Texas and the most northeastern part of Mexico, north to South Dakota, and east into Minnesota and Ohio. ("Megalonaias nervosa", 2011; Clayton, 2012; Haag, 2012; "Megalonaias nervosa", 2014)

What kind of habitat do they need?

The washboard's habitat consists of large slow moving rivers. This mussel is most commonly found in the Mississippi River. The washboard can live in a wide variety of river bottom substances such as mud and rocks, but this mussel prefers to live on gravel or sandy river bottoms. ("Megalonaias nervosa", 2014)

  • Aquatic Biomes
  • benthic
  • rivers and streams
  • Range depth
    15.25 (high) m
    50.03 (high) ft

How do they grow?

After the eggs are fertilized, they move to the female's gills and reside there until the eggs hatch into larvae called glochidia. As a glochidia, the washboard leaves the female's gills and attaches to the gills of fish. The three most common fish that washboards attach to are the flat headed catfish, white crappie and bluegills. Once attached to the fish, the glochidia finish larval development. After larval development is complete, the young washboards release from the gills of the fish and land on the river bottom to mature into adults. Throughout their adult life, the mussels continue to grow. ("Megalonaias nervosa", 2011; Haag, 2012; "Megalonaias nervosa", 2014)

How do they reproduce?

For reproduction, male washboard mussels release sperm into the water and the female washboards take the sperm into their bodies through a tube called the incurrent siphon. When the males release their sperm into the water, this is called spawning. Males spawn when their river water starts to cool down in the fall. ("Megalonaias nervosa", 2011; Cummings and Graf, 2009; Haag, 2012; "Megalonaias nervosa", 2014)

After the eggs are fertilized, the female washboard keeps the eggs in her gills for development. The size of washboard larvae is extremely small, ranging from 50 µm to 450 µm. For the larvae to finish their development, they need to leave their mother and attach to a fish. To make sure this happens, the mother uses a body part called the mantle to act as bait. A fish sees the mantle and thinks that it looks like food, so it swims close to it, not realizing it is a mussel. When the fish gets close enough, the female washboard releases the larvae, and the larvae attach to the gills of the fish. These larvae are now parasites on the fish. The larvae finish development, and drop off and become adult mussels. Larger female washboards usually produce more offspring than smaller female washboards. ("Megalonaias nervosa", 2011; Cummings and Graf, 2009; Haag, 2012; "Megalonaias nervosa", 2014)

  • How often does reproduction occur?
    Washboard individuals breed only once a year.
  • Breeding season
    Spawning takes place in early fall.
  • Range number of offspring
    1,000 to 1,000,000
  • Range age at sexual or reproductive maturity (female)
    3 to 9 years
  • Average age at sexual or reproductive maturity (female)
    8 years
  • Range age at sexual or reproductive maturity (male)
    3 to 9 years
  • Average age at sexual or reproductive maturity (male)
    8 years

Males do not give any parental care, but females do. Females carry the eggs for awhile after they are fertilized while they develop before hatching. The female also uses her body part called the mantle as a lure to attract fish that the larvae will attach to and finish development on. After the larvae leave the mother and attach to the fish, there is no more parental care and the larvae are independent. (Cummings and Graf, 2009)

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

How long do they live?

The oldest recorded washboard was 54 years of age. Typically, washboards live between 30 to 40 years. ("Megalonaias nervosa", 2011; Cummings and Graf, 2009; Haag, 2012)

  • Range lifespan
    Status: wild
    54 (high) years
  • Typical lifespan
    Status: wild
    30 to 40 years

How do they behave?

Washboards may live among other mussels, but they do not interact much with the other mussels after they mature. Adults mostly stay in one spot, but they can move around using a large body part called the foot. Washboards can stick their foot out between the two halves of the shell and push themselves around. The washboard normally moves about during changes in water levels in the rivers. (Haag, 2012; "Megalonaias nervosa", 2014)

How do they communicate with each other?

Washboards get a lot of information about their enviornment based on the temperature of the water. When water temperatures start to cool down, the males will release sperm. Mussels do not really communicate to each other. (Haag, 2012)

What do they eat?

Washboards eat algae, bacteria, protozoans and other organic material. They eat by filter feeding. To filter feed, the mussels take in water through a tube called the incurrent siphon. As the water passes through their gills, food particles and oxygen are removed from the water. Tiny hair-like particles called cilia move the food from the gills to the mouth, while the water leaves the body through another tube called the excurrent siphon. ("Megalonaias nervosa", 2011; Haag, 2012)

  • Plant Foods
  • algae

What eats them and how do they avoid being eaten?

Humans are the largest predator of washboard mussels. Other predators for this mussel include muskrats, raccoons, waterfowl and some fish. ("Megalonaias nervosa", 2011; Haag, 2012; "Megalonaias nervosa", 2014)

What roles do they have in the ecosystem?

Like other freshwater mussel species, washboards are parasites during the early larval stage of life. The larvae of washboards, known as glochidia, live as parasites on fish until they finish developing. Some fish that they attach to include flat headed catfish, white crappie and bluegills.

Zebra mussels (Dreissena polymorpha) are known to attach themselves to washboard mussels, causing the washboard to suffocate and die. Washboards also serve as prey to many predators, such as raccoons and muskrats. This mussel helps make water clearer in some areas by filtering particles out of the water while filter feeding. ("Megalonaias nervosa", 2011; Clayton, 2012; Haag, 2012)

Species (or larger taxonomic groups) used as hosts by this species

Do they cause problems?

Washboards do not cause any problems for humans. ("Megalonaias nervosa", 2014)

How do they interact with us?

People use the shells of washboards for several things. In the pearl industry, the washboard's shell is highly valued for the white inner layer called the nacre. The white nacre is used to make pearls. In the past, buttons for clothing were made out of washboard shells, but this is no longer done. There are other ways to make buttons that do not require any animals be killed. ("Megalonaias nervosa", 2014)

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

Are they endangered?

Washboards are currently a threatened species in several states around the U.S. Habitat destruction is one of the largest factors to the washboards decrease in population size in these states. Pollution, damming of streams, and loss of fish that the larvae need to develop on are also causing washboards to die off. The washboard is also used by the pearl industry, contributing to its population decrease.

Nationally, washboard mussels are not an endangered species. However, knowing that the populations are decreasing in some places, the government and other conservation groups should look into changing the washboard's conservation status. ("Megalonaias nervosa", 2011; Clayton, 2012; Cummings and Graf, 2009; Haag, 2012)


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


2011. "Megalonaias nervosa" (On-line). EOL Encyclopedia of Life. Accessed April 12, 2014 at

Minnesota Department of Natural Resource. 2014. "Megalonaias nervosa" (On-line). Minnesota Department of Natural Resources. Accessed March 20, 2014 at

Clayton, J. 2012. "Mussel Restoration in West Virginia Streams" (On-line). Accessed April 23, 2014 at

Cummings, K., J. Cordeiro. 2011. "Megalonaias nervosa" (On-line). The IUCN List of Threatened Species. Accessed March 20, 2014 at

Cummings, K., D. Graf. 2009. Ecology and Classification of North American Freshwater Invertebrates. Italy: Academic Press.

Haag, W. 2012. North American Freshwater Mussels. New York: Cambridge University Press.

Haggerty, T., J. Garner, R. Rogers. 2005. Reproductive phenology in Megalonaias nervosa (Bivalvia: Unionidae) in Wheeler Reservoir, Tennessee River, Alabama, USA. Hydrobiologia, 539: 131-136. Accessed March 20, 2014 at

Klocek, , Bland, Barghusen. 2008. "Washboard" (On-line pdf). Accessed March 20, 2014 at

Woody, C., L. Holland-Bartels. 1993. Reproductive characteristics of a population of the washboard mussel Megalonaias nervosa (Rafinesque 1820) in the upper Mississippi River. Journal of freshwater ecology. La Crosse, WI, 8/1: 57-66. Accessed March 20, 2014 at

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Brekken, K. 2014. "Megalonaias nervosa" (On-line), Animal Diversity Web. Accessed March 03, 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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