Counting Horseshoe Crabs

Each year the University of Delaware asks for volunteers to help count horseshoe crabs in Delaware Bay.  Counting the number of things that live somewhere is called a census.  In May and June the college does a census during the spawning season so they can estimate how many horseshoe crabs live in the ocean near Delaware.  I first started horseshoe crab counting when I was six years old, and this is my sixth year as a census taker.

Flat Stanley came along to help us.


To count the crabs we use a 1-meter square made of plastic pipe.  We start at one end of a beach, walk 10 meters, put the square on the ground and count how many crabs are in the 1-meter square. We have to keep a separate count of how many male and female crabs are in the square.  We do this 100 times, which means we count over a kilometer of beach.

In the 2006 census at Pickering Beach, DE, we counted 756 total horseshoe crabs in 100 samples.  This means there’s an average of 7.56 horseshoe crabs per sample.  If every meter of the one kilometer beach held the same average of crabs, that would mean that that there were 7,560 horseshoe crabs on the beach.

For more information on horseshoe crabs, visit the Horseshoe Crab Census site at . 


LTC C.J. Wallington
Division Chief
Advanced Technologies, PEO EIS

[submitted by Tory Wallington, fifth grade, Riverside Elementary School, Alexandria, VA]