Mud Crabs

Mud Crab Life

Add the word "mud" to crab, and you come up with not an appealing sounding animal. The goal of this page is to overcome that reputation.

How do mud crabs end up with a crabby reputation? Their first crabby characteristic is their shells. They belong to a crusty group of animals called Crustaceans, which include shrimp and lobsters. This group has a tough outer shell rather than an inner skeleton.

Mud crab photographed at low tide in estuary habitat

Pincers are the second crabby characteristic, possessed by even the quarter-sized mud crab. Each pincer (of which there are two on every crab) is at least twice the size of each of the 8 walking legs. With the pincers, crabs tear into all sorts of food items: live, dead, plant, or animal.

Mud crabs' third crabby characteristic is their enjoyment of living under large rocks sunk into, appropriate enough given their name, soft mud in estuary habitats.

Despite their shells, pincers, and rock-loving habits, mud crabs are amazing animals. Their shells help them cope with daily changes in their world, as dramatic as living upside down one moment and right side up the next. They live in estuaries, areas where ocean water meets fresh water flowing from a river. During part of the day, mud crabs live in steaming muck as the sun beats down. Their shells help to trap water near their gills so that they can still breathe the oxygen from the life-giving liquid. Then during the rest of the day, they live in the freedom of the gently flowing water as the tide comes in.

Even the way they move changes based upon the action of the tides. Above water, they use their eight walking legs (the other 2 being the pincers) to walk sideways. However, underwater they float slightly above the muddy bottom and walk just on the tip of their legs in any direction that they choose.

Most amazing of all to me is that crabs are often one of the first moving ocean animals that children meet. Children usually are able only to go the edge of the sea, so what lives there forms their first impression of marine life. Crabs are the king comical and active dwellers of the area between sea and land, an area of possibilities of bringing together two worlds.

A Quest for Mud Crabs

My husband and I observed mud crabs near Morro Bay's Natural History Museum in Central California in June of 2005. We went right at low tide in the muddy area just to the north of the museum. The fog was clearing on a breezy, cool day.

We found the best place to look was under rocks. We gently lifted up the rocks and then set them down exactly where we found them. We observed mud crabs clinging to sea lettuce on the underside of the rocks. Some mud crabs would be left in the mud as we lifted the rocks. Those skittered sideways to the shadowy part where the rock still met the ground. We had to be especially careful when lowering the rocks in this scenario. Still other crabs would immediately descend into holes; I have since read that mud crabs create long burrows even into the salt marsh area of estuaries.

Mud crabs are most active at night, so apparently we were disturbing their sleep during our daytime visit.

Mud crab at low tide surrounded by algal grasses

The coloring of the mud crabs, a tan or even olive green, initially made it hard to see them. However, once they started waving their pincers defensively or scuttling away, it was easy to observe their behavior.

In the same habitat, we also observed hermit crabs, barnacles, and horn snails.

Crab Symbolism

One of my all-time favorite characters from childhood is Hector Crab from George Sheldon's Oscar Lobster's Fair Exchange. Hector is the sidekick to a fiery and excitable lobster named Oscar who is passionate about rectifying the crime of human beachcombers stealing ocean artifacts like shells and even starfish. Like all classic sidekicks, Hector's personality is opposite of the protagonist's. He trembles at the thought of going up on the beach and wants to live his life peacefully without activism. His only passion is peanut butter and jelly sandwiches. He is such a fearful personality that he had convinced Oscar to move away from their prior home within view of a haunted mansion. In explaining this to a new starfish friend, Hector comments, "My motto is: leave ghosts alone." Eventually Hector does come out of his shell and claims his rightful place as a crab by climbing up into the low tide zone to help Oscar steal items, such as lotion bottles left on the beach, from humans in their own "fair exchange."

Actually Hector is a bit opposite of the traditional symbol of a crab as an animal with persistence, not willing to let go of something in their claws and having the ability to cope with extremes of tide and temperature.

From a Celtic angle, I did not turn up too much research about crabs. An artist created a Celtic crab sculpture featuring designs derived from the Book of Kells in a competition in Baltimore to come up with an emblem for Crabtown.

An Irish proverb states rather cryptically ""Walk straight my son-- as the old crab said to the young crab."

The word "crab" derives from Middle and Old English words meaning "to carve."