Posted by Bernadette Shisler on June 17, 2003

Q: My family and I live in Guam. Every full moon night, land crabs come out of our jungles heading toward the ocean. We would like to know what the full moon and the crabs' movements have to do together. Are they just going for a "swim", or are they heading to the ocean to mate? We have to dodge them as we drive so that we do not crush them. Guam is 12 miles at the widest area. Our roads are not too far from the beaches where these crabs "run" to. Thank you for taking the time to answer this.

A: The moon and the crab's movements are definitely linked. During a full moon, tides are higher than any other time and many marine animals take advantage of this for breeding and egg laying. I'm not well versed on land crabs but I'm quite sure that, just as you've suspected, the crabs are returning to the ocean to mate and lay their eggs. Although land crabs do live on land as adults, their young begin life in the ocean and then crawl out on land as they mature.

John Wiessinger ( June 17, 2003)