In the Twelve Labors of Hercules, Hera sent a giant crab to distract Hercules during his battle with the Hydra.
The Lernaean Hydra was a many-headed water monster living near the springs and marshes of Lerna. While Hercules fought it, Hera sent a huge crab to attack or distract him. Hercules crushed the crab under his foot, then continued the struggle with the Hydra, aided by his nephew Iolaus.
Hera’s intervention reflects her hostility toward Hercules, who was born from Zeus’ relationship with Alcmene. In later mythological tradition, Hera placed the crab among the stars after its death, creating the constellation Cancer.
The crab is sometimes overlooked because the Hydra is the main monster in the episode. It is also easy to confuse this creature with other animals in the labors, such as the Ceryneian Hind, Erymanthian Boar, or Nemean Lion. The crab was not one of the twelve principal creatures Hercules was ordered to capture.