The four species of blue-ringed octopuses are small predators that live in tide pools and shallow rocky reefs throughout the western Pacific and Indian oceans. They reach lengths (including the arms) of only 8-10 inches (20-25 cm) and are named for the bright blue circles that they display on their bodies and arms.
These rings are particularly vivid when an individual is threatened or agitated. In addition to the bright blue rings, these octopuses are famous for having extremely potent venom that can be strong enough to kill a person. There is currently no known anti-venom to treat a person who has been bitten.
The southern blue-ringed octopus is restricted to the southern coast of Australia, where it feeds primarily on small crustaceans, including shrimps and crabs. It can use its venom to immobilize its prey by either of two methods: 1) biting the prey and injecting the venom directly into the wound or 2) releasing a cloud of venom into the water which enters potential prey through its gills. Southern blue-ringed octopuses are only a threat to humans when they feel threatened and directly bite someone.
Southern blue-ringed octopuses reproduce through internal fertilization, and a female lays benthic eggs that she guards until they hatch, sometimes as long as several months. During this time, she does not leave her nest to feed or for any other reason. Like all octopuses, southern blue-ringed octopuses are short-lived, and females only reproduce once in their lifetime. While guarding the eggs, females become weak, and they die soon after the eggs hatch.
Population trends of the blue-ringed octopuses are unknown. They are not targeted for human consumption, but some individuals may be captured for the private aquarium trade. As they live in very shallow waters, they may be vulnerable to changes resulting from coastal development or other human activities. One of the four species of blue-ringed octopuses was described based on only a single specimen captured in the Bay of Bengal, and some scientists question whether or not that individual should be considered its own species.