incremental layers, thought to be laid down on a daily basis. This has enabled researchers to estimate growth rates, ages, and age to maturity. Chironex fleckeri, for example, increases its inter-pedalia distance (IPD) by per day, reaching an IPD of when 45 to 50 days old. The maximum age of any individual examined was 88 days by which time it had grown to an IPD of . In the wild, the box jellyfish will live up to 3 months, but can survive up to seven or eight months in a science lab tank. Behavior The box jellyfish actively hunts its prey (small fish), rather than drifting as do true jellyfish. They are capable of achieving speeds of up to 1.5 to 2 metres per second or about . The venom of cubozoans is distinct from that of scyphozoans, and is used to catch prey (small fish and invertebrates, including prawns and bait fish) and for defence from predators, which include the butterfish, batfish, rabbitfish, crabs (blue swimmer crab) and various species of turtle including the hawksbill sea turtle and flatback sea turtle. It seems that sea turtles are unaffected by the stings because they seem to relish box jellyfish. Danger to humans Although unspecified species of box jellyfish have been called in newspapers "the world's most venomous creature" and the deadliest creature in the sea, only a few species in the class have been confirmed to be involved in human deaths; some species are not harmful to humans, possibly delivering a sting that is no more than painful. Australia In Australia Hugo Flecker, who worked on various venomous animal species and poisonous plants, was concerned at the unexplained deaths of swimmers. He identified the cause as the box jellyfish later named Chironex fleckeri. In 1945, he described another jellyfish envenoming which he named the "Irukandji Syndrome", later identified as caused by the box jellyfish Carukia barnesi. In Australia, fatalities are most often caused by the largest species of this class of jellyfish, Chironex fleckeri, which is certainly one of the world's most venomous creatures. After severe Chironex fleckeri stings, cardiac arrest can occur quickly, within just two minutes. In Australia, C. fleckeri has caused at least 79 deaths since the first report in 1883, but even in this species most encounters appear to result only in mild envenoming. While most recent deaths in Australia have been in children, including a