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Common Spider Crab

Libinia emarginata

The shell of the common spider crab measures about four inches from front to back. When its legs are stretched out, the spider crab can reach a spread of one foot. (joo0ey/Flickr)
The shell of the common spider crab measures about four inches from front to back. When its legs are stretched out, the spider crab can reach a spread of one foot. (joo0ey/Flickr)

Also known as the portly spider crab or the nine-spined spider crab, the common spider crab is a long-legged and slow-moving crustacean that covers itself in algae and small debris as a defense against predators. 

Appearance:

  • Khaki-colored, triangle-shaped carapace (shell)
  • Tapered snout and short eyestalks
  • White, narrow claws that are slow and not very strong
  • Males grow larger than females
  • When legs are outstretched, common spider crab can reach a spread of up to one foot
  • Carapace measures about four inches from front to back, and features median row of nine low spines (which differentiate the creature from the six-spined spider crab)
  • Carapace is often ornamented with various spines and tubercles, and clothed in algae, debris and small invertebrates held in place by hook-like hairs 

Habitat:

  • Found on a variety of ocean, bay or harbor bottoms, from shallow water to depths exceeding 150 feet

Range:

  • Inhabit the brackish and salty waters of the Chesapeake Bay, from Washington, D.C., to the Bay's mouth
  • Found from Nova Scotia to the western Gulf of Mexico 

Feeding:

  • Sluggish and unaggressive scavengers with poor eyesight
  • Sensitive tasting and sensing organs located on the tips of its walking legs allow common spider crab to identify food in the water or mud as it walks
  • Often feed on large starfish 

Predators:

  • Main defense against predation is ability to camouflage itself with various spines and tubercles, algae, debris and small invertebrates 
  • When startled, will wave pincers over head in warning gesture 

Reproduction and Life Cycle:

  • Must molt to grow
  • When molting, common spider crab clings to top of eelgrass close to water's surface
  • Have been observed molting in large "pods" in the fall, hibernating in dense patches in the winter and mating in large groups in the spring 
  • Females close to releasing eggs are held behind male and aggressively protected
  • Young hatch from eggs that are bright orange-red when laid but turn brown during development, which takes about 25 days 

Other Facts:

  • Tolerant of pollution and eutrophic environments, or environments in which there is little oxygen 
  • Often walks in a forward motion, although is capable of side-stepping like other crabs 

Sources and Additional Information:




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