Animal Diversity Web

Ge­o­graphic Range

The Sand fid­dler crab is one of three Uca species, which are found from Cape Cod to Texas with the ex­cep­tion of Florida and south of St. Au­gus­tine. The lo­ca­tions of the crabs are usu­ally near the coastal marshes or near in­ter­tidal zones.

(NOAA Costal Ser­vices Cen­ter 2001)

• Biogeographic Regions
• nearctic
  • native

Habi­tat

Fid­dler crabs are found in strongly brack­ish to salt­wa­ter salin­i­ties all along the east­ern seaboard. They live in low marshes, which have sed­i­ments that are cov­ered by water on most high tides, char­ac­ter­ized pri­mar­ily by salt­marsh cord­grass. Uca pugi­la­tor each live in a hole or bur­row that it digs for it­self. The bur­row can be closed with a mud cap for se­cu­rity. Dur­ing low tide fid­dler crabs aban­don its dwelling to search for food, but never strays very far un­less it is to court a fe­male or scare away a neigh­bor.

(Priest 2000)

• Aquatic Biomes
• coastal

Phys­i­cal De­scrip­tion

The Sand fid­dler crab is ap­prox­i­mately 1.5 inches(38mm) wide and 1.0 inch(25mm) long. All fid­dler crabs are sim­i­lar in shape, hav­ing a smooth cara­pace and a square-shaped body. The eyes are found at the ends of two long and slen­der, mov­able eye­stalks lo­cated in the cen­ter of the cara­pace. Male fid­dler crabs are brighter in color, hav­ing a pur­ple grey or blue cara­pace with ir­reg­u­lar mark­ings of black or brown. The fe­males have equal-sized claws and gen­er­ally have a much more sub­dued col­oration on their cara­paces. Being that they are crabs they are con­sid­ered de­capods or an­i­mals with ten limbs; al­though both of their claws are not re­ferred to as legs, they are ac­tu­ally che­lipeds or claws. Males have a com­mon char­ac­ter­is­tic of one large pin­cer. This pin­cer, which is usu­ally brightly col­ored, can ei­ther be on the right or left side and is at least four times larger than the other. The large che­liped can be as fifty per­cent as mas­sive as the rest of the male com­bined. Uca pugi­la­tor use the large claw to de­fend their bur­rows and at­tract mates. Fid­dler crabs even get their name from the male's large claw.

(He Zhong 2001)

• Other Physical Features
• ectothermic
• bilateral symmetry

Re­pro­duc­tion

Breed­ing oc­curs ap­prox­i­mately every two weeks for most of the sum­mer. Re­pro­duc­tion oc­curs in bur­rows sim­i­lar to the ones Uca pugi­la­tor live in only larger and bet­ter-main­tained. The two crabs mate and then two weeks later after the in­cu­bat­ing of the eggs for the night will re­turn to the sur­face and re­lease her eggs into the water where they de­velop. The fe­male when at the water ex­trud­eds all of her fer­til­ized eggs, which can be as many as a quar­ter mil­lion, onto her ab­dom­i­nal flap in one small spongy clus­ter. The eggs will hatch after sev­eral months and will be re­leased into the near­est tidal creek dur­ing high tide where again after sev­eral months the young fid­dler crabs un­dergo meta­mor­pho­sis and change into their final form. These new adult crabs re­turn to the land for the rest of their lives.

(Priest 2000)

Be­hav­ior

Fid­dler crabs are colo­nial, often liv­ing to­gether in large clus­ters. Ter­ri­to­r­ial fight­ing oc­curs be­tween the males, and they will go to ex­tremes to de­fend their bur­rows. De­spite their fight­ing, they travel in herds of thou­sands when feed­ing. The process of re­pro­duc­tion be­gins by males stand­ing at the edge of their bur­rows, usu­ally lin­ing up with other males only cen­time­ters away. Then, as a fe­male ap­proaches the male crab of her choos­ing, the male will wave the large che­liped vig­or­ously. If the fe­male is still in­ter­ested, the male will then run to­ward her, back to the bur­row, back to her, and back to the bur­row again to show which bur­row is his. The male fi­nally drums his large che­liped against the sides of the bur­row until she en­ters. Upon her en­trance the male crab seals the bur­row with a mud cap for mat­ing.

(He Zhongn 2001)

Food Habits

Sand Fid­dlers in­gest par­ti­cles of sand or mud and they use their mouth­parts to scrape food ma­te­ri­als from the sed­i­ment, and then de­posit the sed­i­ment back down on the ground as a "feed­ing pel­let." The ac­tual method of con­sump­tion oc­curs when the scooped mud is put in their mouths and the en­trapped de­tri­tus is fil­tered out using spe­cial­ized brush-like mouth­parts. Water is pumped from their gills into their mouths to float the de­tri­tus free of the mud. The food ma­te­r­ial con­sists of de­cay­ing or­ganic mat­ter or uni­cel­lu­lar plants such as algae. The che­lipeds are used for pick­ing up the small amounts of sed­i­ment not for crush­ing things or for a grip. Be­cause of one en­larged claw the males can­not eat as fast as fe­males so they have to eat twice as fast.

(Priest 2000)

Eco­nomic Im­por­tance for Hu­mans: Pos­i­tive

Uca pugi­la­tor are not only im­por­tant reg­u­la­tors of cord­grass but also are im­por­tant to the food­web. They are eaten by larger preda­tors, such as blue crab, rails, egrets, herons, and rac­coons. Fid­dler crabs also stim­u­late the turnover and min­er­al­iza­tion of im­por­tant nu­tri­ents. They can even be a good en­vi­ron­men­tal in­di­ca­tor to en­vi­ron­men­tal con­t­a­m­i­nates es­pe­cially in­sec­ti­cides.

(He Zhong 2001)

Eco­nomic Im­por­tance for Hu­mans: Neg­a­tive

Growth of marsh grasses can be af­fected by their ac­tiv­ity. Uca pugi­la­tor can erode or un­der­mine marsh­banks by bur­row­ing and feed­ing.

(He Zhong 2001)

Con­ser­va­tion Sta­tus

• IUCN Red List

  No special status

• US Federal List

  No special status

• CITES

  No special status

Other Com­ments

A very unique qual­ity of Uca pugi­la­tor is that they are able to re­gen­er­ate lost limbs. Re­gen­er­a­tion is based on two growth stages, basal and proecdysial. The first stage of growth, basal growth, is due to the in­crease of cell num­ber by mi­totic di­vi­sion of the blastemal cells. The sec­ond stage or proecdysial growth is due to the in­crease in cell size by pro­tein syn­the­sis and water up­take. It usu­ally takes many months to com­plete full re­gen­er­a­tion and the new pin­cer is nor­mally not as large nor as strong as the orig­i­nal.

( Chung 2001)

Con­trib­u­tors

Chris Pat­ter­son (au­thor), West­ern Mary­land Col­lege, Louise a. Paquin (ed­i­tor), West­ern Mary­land Col­lege.

Ref­er­ences

Chung, A. "Bi­o­log­i­cal Sci­ences" (On-line). Ac­cessed April 14, 2001 at http://​gradweb.​ou.​edu/​Poster/​Biological.​html.

Priest III, W. Fall 2000. Wet­land Denizens Fid­dler Crab. The Vir­ginia Wet­lands Re­port, 15: 3,5.

Zhong, H. 2001. Com­mon Florida Fid­dler Crabs (*Uca* spp.). Pub­lic Health En­to­mol­ogy Re­search & Ed­u­ca­tion Cen­ter, 10: 4.