You might not know this, but during the late 1970’s, your grandparents regularly dressed like this:

…so they could go out in public and try to dance like this:

Though fiddler crabs rarely dress like your grandparents did in the late 1970s, they do dance like your grandparents used to. See?

This disco-dancing fiddler crab is a male. It’s easy to tell the difference between a male fiddler crab and a female fiddler crab. Males are the ones that have one giant claw and one little claw. Females have two little claws.

The main purpose of that gigantic claw is to help male fiddler crabs impress female fiddler crabs through disco-dancing. The males wave their big claws back and forth and the one with the best moves is the one that gets the girls. I’m not kidding. If you visit a salt marsh in summertime at low tide, you may see hundreds of male fiddler crabs waving their claws back and forth and the girls are just walking around looking at them.

Why do fiddler crabs disco-dance? At some point, most male animals want to have a girlfriend, because, eventually, it leads to them becoming fathers. One way to get a girl's attention is by showing off. Males of many animal species have different ways of showing off to meet females, including…

...male cardinals with their bright red color…

...male bighorn sheep that like to bash their heads together…

...and your teenage brother.

To learn more about fiddler crabs, read my book A Day in the Salt Marsh.

Also, make sure you ask your grandparents to show you their disco-dancing moves.

Online references and resources:

Encyclopedia of Life. "Uca: Fiddler Crabs."
      http://eol.org/pages/15178/details
South Carolina Department of Natural Resources. "Fiddler Crabs."
      https://www.dnr.sc.gov/cwcs/pdf/FiddlerCrab.pdf
The University of Southern Mississippi: Gulf Coast Research Laboratory. "Fiddler Crabs of the Northern Gulf Coast."
      http://gcrl.usm.edu/public/gulf.creatures/fiddler.crabs/fiddler.crabs.php
Virginia Institute of Marine Science. "Fiddler Crabs."
      http://www.vims.edu/research/departments/eaah/programs/crustacean/research
      /fiddler_crabs/index.php

Photos and Images:

Click the photos, images and GIFs used above to find their sources.