Ghost Crabs and Fiddler Crabs

     Over the years, I have seen interesting colonies of fiddler crabs at such distant places from each other as in sand at the Wetlands Institute in salt marshes at Stone Harbor, New Jersey, along the muddy shores of the brackish Delaware River at Delaware City in the state of the same name, and along the salty edges of a bay by the Atlantic Coast at Charleston, South Carolina.  I saw those two-inch-wide crabs during the day as they went about their business of feeding and courting.  And, of course, the most amazing part of seeing those crabs was the huge front claw on each male.  Claws they use to attract females and intimidate other males.
     While reading about fiddler crabs, I learned they are related to ghost crabs and have several characteristics in common with them.  Both species swiftly run sideways and live in burrows they dig themselves.  Both use front claws to shuttle food to their mouths, can live as long as two years and are about two inches across at maturity.  Each species sheds its shell several times as it grows, has two stalked eyes and breathes oxygen from the air by moist gills.  Both kinds are eaten by gulls, herons and other predators.  Males of both kinds compete ritually for the attention of receptive females and females of both types release eggs into water.  And one of the two front claws of both species is larger than the other.   
     Atlantic ghost crabs live in burrows up to four feet deep on sandy beaches, above the normal high tide line, along the Atlantic and Gulf Coasts from Maine to southern Brazil.  Each tunnel has a living chamber at the end of it and a second burrow out so the crab isn't trapped in its own home.
     These ghost crabs are yellow or pale gray, the reason they are called "ghosts", to blend into their sandy habitat when abroad in search of food, especially during the day, though they are mostly nocturnal.  They ingest small clams, insects, baby sea turtles that hatched on certain beaches, decaying plants and detritus.
     Male ghost crabs make sounds by stamping their legs on the sand, probably as part of their courtship rituals.  And one front claw on both genders of this species is a bit larger than the other.  The related male fiddlers evolved that larger claw trait to its maximum.  They probably couldn't lift or carry that greatly enlarged front claw if it got any larger than it already is.
     Colonies of many fiddler crabs live on sandy beaches and brackish, tidal mud flats.  Each one has its own burrow, making the sand or mud look like Swiss cheese.  Fiddlers are active and quite visible during the day, if one knows when and where to look for them.  At that time they pick up little blobs of sand or mud with their smaller front claws and pass those materials to their mouths.  They glean alga, fungus, microbes and detritus from each mouthful of sand or mud and discharge little balls of the inedible materials.         
     Each adult male fiddler crab has one front claw that is much bigger than the other one, and about as large as his body.  He can't use it to shuttle food to his mouth, but he waves it in the air to beckon females of his kind to come to him for mating.  Female fiddlers choose to mate with a male with the biggest  front pincer and who most vigorously waves it, indicating the male's strength and health that he will pass along to his offspring.  The females' selections over many years promoted the evolution of the large claws on male fiddler crabs, though it is dangerous to be so obvious.
     Both these species of crabs are interesting to experience.  And since they evolved from a common ancestor, they are another example of function and structure changes that help insure survival.