According to Elle Di Jensen at Paw Nation, a female hermit crab lays between 800 and 50,000 eggs at a time. This number depends on her size, with larger ones laying more and smaller ones laying fewer.
As The Hermit Crab Patch explains, a female hermit crab's eggs are laid and deposited with the aid of the gill grooming appendages along the left side of her abdomen. She carries her eggs as they mature for approximately 1 month, and during that time, the eggs change color from brick red to dark gray as the embryos deplete their yolk supply. Hermit crabs have a lifespan of 40 or more years.