According to the Maryland Department of Natural Resources, crabs become “soft shell” crabs when they molt. After going through that process, their new shell is pliable and easily stretched. Large amounts of water are consumed prior to and shortly after the molt, causing the soft shell to expand and increase in size. This entire process takes two to three hours and within two hours after the old shell is shed, the new one begins to harden.
Recently, the Coastal Explorations touring company in Corolla, North Carolina posted a time lapse molting video on Facebook of their resident crab, Jimmy.