Marsh Crab

Sesarma reticulatum

Quick Facts

  • Species

    Native

  • Habitat

    Marsh crabs are found in salt and brackish cordgrass marshes and nearby mud flats. Lives communally within interconnected burrows in the mud. Burrows are 25 to 30 inches deep and usually filled with water. Burrow entrances, which may be an inch or more in diameter, are located near the high-tide line. Marsh crabs are most active at night.

  • Range

    Found throughout the middle and lower Chesapeake Bay, ranges as far north as Arundel on the Bay near Annapolis, Maryland.

  • Diet

    Marsh plants

  • Status

    Stable

The marsh crab is a small shore crab that lives in salt and brackish marshes in the middle and lower Chesapeake Bay.

Appearance

The marsh crab has a small, square carapace (shell) that grows to one inch wide and varies in color from warm brown to dark olive. Its eyes are on stalks located at the front corners of its body. It has two teeth toward the front on either side of the carapace and a notch along the middle of the carapace. It has furry terminal joints on its first three walking legs.

Feeding

Marsh crabs eat the outermost leaves of marsh plants, especially cordgrass, and will sometimes prey upon fiddler crabs. 

Predators

Black-crowned night herons are known predators. 

Voice

Although the marsh crab does not produce vocal sounds, they do exhibit acoustic behavior. Male marsh craps produce a tapping sound to defend their burrows and to engage in mating with females. Males produce this sound by striking two of their legs together. According to a study published in the journal Crustaceana, “the sounds recorded on a tape recorder in the laboratory consisted of six to 29 taps (tongs contacts) and there was an interval of about a third of a second between taps.”

Reproduction and Life Cycle

Little is known about the marsh crab life cycle. Females may carry 5,000 to 13,000 eggs at a time and breed up to five times in her lifetime. Their mating behavior includes a courtship tapping ritual, in which the males will tap the female and create drumming sounds with their walking feet. Mating ends with an indirect sperm transfer. 

Did You Know?

  • The marsh crab is also known as the purple marsh crab, the square-backed marsh crab and the heavy marsh crab.
  • Males are known for making “rapping” sounds when defending their burrow.
  • They have been linked to large losses of cordgrass in marshes on Cape Cod, Massachusetts, due to overeating.

Sources and Additional Information

Quick Facts

  • Species

    Native

  • Habitat

    Marsh crabs are found in salt and brackish cordgrass marshes and nearby mud flats. Lives communally within interconnected burrows in the mud. Burrows are 25 to 30 inches deep and usually filled with water. Burrow entrances, which may be an inch or more in diameter, are located near the high-tide line. Marsh crabs are most active at night.

  • Range

    Found throughout the middle and lower Chesapeake Bay, ranges as far north as Arundel on the Bay near Annapolis, Maryland.

  • Diet

    Marsh plants

  • Status

    Stable