Spider Crabs stick together as they squeeze off their old, hardened shells and expose their new soft shells that allow them to grow in size. As 'gardeners' of the sea, they feed on all the Algae and sponge. Once the Crabs fully moult, they're actually open to being predated on by stingrays and other sea creatures.
The Spider Crabs symbolically represent resiliency, unwillingness to give up, renewal and rebirth.
The Chinese regard the Crab as a harbinger of good luck