This horseshoe crab molt measures 11.5 inches long including the tail. Our horseshoe crab molts are collecting by us in the salt water river leading out to the ocean near our home on the north shore of Massachusetts. They start to appear the third week of July, we find them floating on the water in the river. A horseshoe crab molt is the process by which a horseshoe crab sheds its exoskeleton to grow. Horseshoe crabs shed several times in their lifetime. No animal was harmed in the process of us collecting these molts. You will receive the horseshoe crab in the photograph.