Giant crabs are seen as large monsters in far of countries they in fact are oversized crabs. Although the origins for these giant crabs may not be so mythological or made up as crabs have a rare ability is that they don't really die from old age if protected and in the right environment they can keep growing. Large crabs have been found that are over a metre in width (which in its self is huge compared to ones you see on the beach about 2-8cms in width). In times when we humans didn't pollute the sea as much and these crabs had all the time to grow, you never know.