Greek Myth
The myth that the Greeks used to explain the heavenly crab involved the great Hercules, along with the obsessive hatred and jealousy that the Queen of the Gods, Hera, held for him.
Celestial Crab
According to Greek myth, Hera implored a giant crab to grab Hercules by the heel as Hercules was fighting the monstrous Hydra to the death. After Hercules crushed the crab, Hera transformed it into a group of stars to reward its loyalty to her.
Egyptian Myth
The Egyptians saw this part of the sky as a giant scarab beetle, which rolled the sun across the heavens much as the real insect will roll dung along the ground.
Babylonian Myth
Babylonian culture felt that the area Cancer occupied in the sky was akin to a gateway from which souls would descend from heaven and go into people's bodies.
Moon
The astrological sign of the Crab links closely to the moon, with the thinking being that the moon influences the tides, which has a direct effect on crabs.