The tiny blue-ringed octopus, ironically for its size, is the most deadly of all cephalopods.
When alarmed, it displays small blue rings that generally measure less than 2mm in diameter. The blue-ringed octopus is about the size of a pea when hatched then grows to reach the size of a golf ball. It weighs only 28 grams with a body up to 5cm long and arms up to 10cm.
The blue-ringed octopus can be found only in the temperate waters of southern Australia, from southern Western Australia to eastern Victoria at depths ranging from 0-50 metres. It feeds on small crabs, hermit crabs, and shrimp that it hunts during the day.
Two types of poison secreted by two separate poison glands are used against prey and predators. One of the poisons is used for hunting crab, and the other – which is extremely toxic – is used as self defense against predators.