The Irukandji jellyfish are any of several similar, extremely venomous species of rare box jellyfish. With a very small adult size of about a cubic centimetre, they are both one of the smallest and one of the most venomous jellyfish in the world. They inhabit the northern marine waters of Australia, and cost the Australian government $AUD 3 billion annually through tourism losses and medical costs associated with stings. This type of jellyfish reproduces sexually with eggs and sperm. They fire their stingers into their victim, causing a condition known in humans as Irukandji syndrome, which can be fatal and difficult to immediately recognise due to the delayed effects of the venom. There are about 16 known species of Irukandji, of which Carukia barnesi, Malo kingi, Malo maxima, Malo filipina and Malo bella are the best known.