Editing Crab (section)

==Behaviour==
[[File:Carpilius convexus is consuming Heterocentrotus trigonarius in Hawaii.jpg|left|thumb|''[[Carpilius convexus]]'' consuming ''[[Heterocentrotus trigonarius]]'' in Hawaii]]
Crabs typically walk sideways<ref name="Sleinis">{{cite journal |title=Locomotion in a forward walking crab |author1=Sally Sleinis |author2=Gerald E. Silvey |journal=Journal of Comparative Physiology A |volume=136 |issue=4 |year=1980 |doi=10.1007/BF00657350 |pages=301–312|s2cid=33455459 }}</ref> (hence the term [[wikt:crabwise|crabwise]]), because of the articulation of the legs which makes a sidelong gait more efficient.<ref name="Vidal-Gadea">{{cite journal |title=Skeletal adaptations for forward and sideways walking in three species of decapod crustaceans |author1=A. G. Vidal-Gadea |author2=M.D. Rinehart |author3=J.H. Belanger |journal=[[Arthropod Structure & Development]] |volume=37 |issue=2 |date=March 2008 |pmid= 18089130 |pages=179–194 |doi=10.1016/j.asd.2007.06.002|bibcode=2008ArtSD..37...95V }}</ref> Some crabs walk forward or backward, including [[Raninidae|raninids]],<ref>{{cite web |title=Spanner crab ''Ranina ranina'' |url=http://www.dpi.nsw.gov.au/fisheries/recreational/saltwater/sw-species/spanner-crab |publisher=[[New South Wales Department of Primary Industries]] |access-date=2009-01-04 |year=2005 |work=Fishing and Aquaculture}}</ref> ''[[Libinia emarginata]]''<ref>{{cite journal |title=Muscular anatomy of the legs of the forward walking crab, ''Libinia emarginata'' (Decapoda, Brachyura, Majoidea) |author1=A. G. Vidal-Gadea |author2=J. H. Belanger |journal=[[Arthropod Structure & Development]] |volume=38 |issue=3 |year=2009 |pmid=19166968 |pages=179–194 |doi=10.1016/j.asd.2008.12.002|bibcode=2009ArtSD..38..179V }}</ref> and ''[[Mictyris platycheles]]''.<ref name="Sleinis"/> Some crabs, like the [[Portunidae]] and [[Matutidae]], are also capable of swimming,<ref name="Ng">{{cite journal|journal=[[Raffles Bulletin of Zoology]] |year=2008 |volume=17 |pages=1–286 |title=Systema Brachyurorum: Part I. An annotated checklist of extant Brachyuran crabs of the world |author=Peter K. L. Ng, [[Danièle Guinot]] & Peter J. F. Davie |url=http://rmbr.nus.edu.sg/rbz/biblio/s17/s17rbz.pdf |url-status=dead |archive-url=https://web.archive.org/web/20110606061453/http://rmbr.nus.edu.sg/rbz/biblio/s17/s17rbz.pdf |archive-date=2011-06-06 }}</ref> the [[Portunidae]] especially so as their last pair of walking legs are flattened into swimming paddles.<ref name="Weis" />{{rp|96}}

Crabs are mostly active animals with complex behaviour patterns such as communicating by drumming or waving their [[Chela (organ)|pincers]]. Crabs tend to be aggressive toward one another, and males often fight to gain access to females.<ref>{{cite book |chapter=Crab (animal) |title=Encarta |year=2005 |publisher=[[Microsoft]]|title-link=Encarta }}</ref> On rocky [[shore|seashores]], where nearly all caves and crevices are occupied, crabs may also fight over hiding holes.<ref>{{cite book |title=The Miles Kelly Book of Life |location=[[Great Bardfield]], [[Essex]] |publisher=[[Miles Kelly Publishing]] |year=2006 |pages=512 |isbn=978-1-84236-715-5}}</ref> [[Fiddler crab]]s (genus ''Uca'') dig burrows in sand or mud, which they use for resting, hiding, and mating, and to defend against intruders.<ref name="Weis"/>{{rp|28–29, 99}}

Crabs are [[omnivore]]s, feeding primarily on [[alga]]e,<ref>{{cite journal |doi=10.1080/00288330.1993.9516571 |title=Natural diet of the crab ''Notomithrax ursus'' (Brachyura, Majidae) at Oaro, South Island, New Zealand |author=Chris M. C. Woods |journal=[[New Zealand Journal of Marine and Freshwater Research]] |year=1993 |volume=27 |pages=309–315 |issue=3 |bibcode=1993NZJMF..27..309W |doi-access=free }}</ref> and taking any other food, including [[mollusc]]s, [[worm]]s, other [[crustacean]]s, [[fungi]], [[bacteria]], and [[detritus]], depending on their availability and the crab species. For many crabs, a mixed diet of plant and animal matter results in the fastest growth and greatest [[fitness (biology)|fitness]].<ref>{{cite journal |author=Robin Kennish |year=1996 |title=Diet composition influences the fitness of the herbivorous crab ''Grapsus albolineatus'' |journal=[[Oecologia]] |volume=105 |issue=1 |pages=22–29 |doi=10.1007/BF00328787|pmid=28307118 |bibcode=1996Oecol.105...22K |s2cid=24146814 }}</ref><ref>{{cite journal |title=Diet choice in an omnivorous salt-marsh crab: different food types, body size, and habitat complexity |author1=Tracy L. Buck |author2=Greg A. Breed |author3=Steven C. Pennings |author4=Margo E. Chase |author5=Martin Zimmer |author6=Thomas H. Carefoot |journal=[[Journal of Experimental Marine Biology and Ecology]] |year=2003 |volume=292 |issue=1 |pages=103–116 |doi=10.1016/S0022-0981(03)00146-1|bibcode=2003JEMBE.292..103B }}</ref> Some species are more specialised in their diets, based in plankton, clams or fish.<ref name="Weis"/>{{rp|85}}

Crabs are known to work together to provide food and protection for their family, and during mating season to find a comfortable spot for the female to release her eggs.<ref>{{cite journal |author=[[Danièle Guinot]] & J.–M. Bouchard |year=1998 |title=Evolution of the abdominal holding systems of brachyuran crabs (Crustacea, Decapoda, Brachyura) |journal=[[Zoosystema]] |volume=20 |issue=4 |pages=613–694 |url=http://www.mnhn.fr/publication/zoosyst/z98n4a4.html |format=[[Portable Document Format|PDF]] |url-status=dead |archive-url=https://web.archive.org/web/20061118171555/http://www.mnhn.fr/publication/zoosyst/z98n4a4.html |archive-date=2006-11-18 }}</ref>