How long does it take a moon crab to grow a limb back?

How long it takes a hermie to regrow a lost leg depends on many factors. In order to grow a leg back, they must first begin to grow the new leg as a gel limb. This will be a clear to whitish little blob that will eventually become a whole leg. They then will need to molt. Molting is when they are growing larger and outgrow their exoskeleton (hard outer skin). They will need to load up on water (especially salt water) and food, then bury in damp sand to shrug off their old skin and start growing their new skin. They will eat the old skin to help grow the new skin. After a little while, they will emerge from the sand with shiny new skin. The amount of time it takes for a molt depends on the conditions it is molting in, how long they have gone since the last molt and the overall health and size of the crab. A grape-sized crab can take anywhere from 2 weeks to over a month to do this, where a lemon sized crab could take 3 or four months or more! While a crab can grow a whole new leg in only one molt (I just had a large do this), the new leg may be shorter and/or thinner than the others and it may take as many as 3 molts to get it back to where it was before in terms of size & strength.