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Is that a Crab?! Crabs in Camouflage

Did you know that many crustaceans use camouflage to hide from predators? When visiting the Coastal Bays be sure to pay attention to your surroundings, you might just see one of these common crab species hiding in plain sight!

Common Spider Crab

Common Spider Crab
Spider Crab, Photo by Chandler Joiner

One crab species in Maryland’s Coastal Bays that has mastered the art of camouflage is the Common Spider Crab. The Common Spider Crab, also known as the Portly Spider Crab or the Nine-spined Spider Crab, is a long-legged, extremely slow-moving crustacean that belongs to a group of crabs known as “decorator crabs.” Decorator crabs’ main line of defense against predators are their unique ability to camouflage by “decorating” themselves with a variety of debris, plants, and animals. Common Spider Crabs have various spines and tubercles (rounded protruding bones) that are great camouflage, but they also cover themselves in algae, shell pieces, small debris, seaweed, and various tiny invertebrates to avoid detection from predators. These items are held onto the Spider Crab’s shell by fine, sticky, hook-like hairs covering their bodies. The most common predators of Spider Crabs are gulls and other shore birds, and various fish and sharks. So, if you ever see a slow moving “rock” on the bottom of the Bay floor, it might just be a beautifully decorated Spider Crab!

Fun fact: When a Common Spider Crabs legs are fully outstretched, they can be up to one foot in size!


Atlantic Mud Crab

Mud Crab, Photo by Liz Wist

Another crab with innate camouflage capabilities is the Atlantic Mud Crab. These small crustaceans are a muddy brown color with black-tipped claws that are distinctly unequal in size. Mud crabs are frequently found living in the muddy bottoms of marshes, throughout oyster beds, and often under stones, shells, and along masses of sponges. The color of Atlantic Mud Crabs closely matches the appearance of the mud they so frequently live in, making them extremely difficult to see. When predators are near, they can easily become indistinguishable by burying themselves in the muck of the bay floor. This camouflage is very important because one of the mud crabs primary predators is the Oyster Toadfish, which is a bottom dwelling fish species that is always on the prowl.

Fun Fact: The Atlantic Mud Crab is the largest of the mud crab species in the Coastal Bays area, measuring in at three-quarters of an inch wide and one and a half inches long… so imagine the small size of the other mud crab species!


Ghost Crab, Photo by C. Joiner

Atlantic Ghost Crab

This incredibly active “terrestrial” crab can be found darting and dashing along coastal beaches from Delaware all the way down to Brazil. Their beautiful sand-colored bodies and stark white claws allow them to easily blend in with the sand around them and escape detection. Atlantic Ghost Crabs can easily flatten their bodies just under the surface of the sand and their sandy coloration makes them almost impossible to spot. They also dig burrows in the sand to seek shelter from the sun and predators – these burrows can be about four feet deep! The reason Atlantic Ghost Crabs are considered more terrestrial than any other crab species is because they do not have to return to the water to wet their gills (even though some do). They can simply wick up water from the damp sand using fine hairs located on the base of their legs to wet their gills or they brace on the sand and allow incoming waves to wash over their bodies.

Fun Fact: Atlantic Ghost Crabs can rotate their large club-shaped eyes 360 degrees around!



About the MCBP contributor:

Chandler Joiner is an Environmental Educator with the Maryland Coastal Bays Program. She is responsible for developing and leading a variety of environmental education programs, including newly added virtual programming for students and community members. Chandler is also responsible for the creation and implementation of MCBP’s Living Local program. Click here to check out the Living Local farm spotlights, and if you are interested in registering for a Living Local farm visit, please email cjoiner@mdcoastalbays.org for more information.

Maryland Coastal Bays Program
Maryland Coastal Bays Programhttp://mdcoastalbays.org
All Creature Features are written by a Maryland Coastal Bays Program (MCBP) staff member.  MCBP is a non-profit and National Estuary Program that exists to protect and conserve the waters and surrounding watershed of Maryland’s coastal bays to enhance their ecological values and sustainable use for both present and future generations. MCBP works with stakeholders on the local, state, and federal level to protect the five main bays within the watershed; Assawoman, Isle of Wight, Sinepuxent, Newport, and Chincoteague, through restoration, environmental education, scientific monitoring, and targeted community outreach.

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