This very small
octopus (reaching up to 100 g and 20 cm across spread tentacles) can be
found from Japan to Australia in shallow tropical water and in tide pools,
where it hunts for crabs (its main pray). It is normally yellowish brown
but when disturbed, the octopus changes its rings to a bright blue thus
showing its change of mood.
The venom of the blue-ringed
octopus is contained in its saliva, which is produced by a couple of glands
that have the same size as the brain of the animal. The venom has two components.
One of them is probably most effective on crabs but relatively harmless
to humans. The other one is the same as the toxin present in the puffer
fish (tetrodotoxin) and probably serves as a defense against predatory
fish. The bite is usually painless but this octopus has
venom. It is not injected but enters the wound in saliva. People soon notice
numbness around the mouth followed by paralysis.
Death results from respiratory
failure. The victim might be saved if artificial respiration starts before
marked cyanosis (heart condition causing blueness of the body surface)
and hypotention develop.
Since the blue-ringed octopus
is typically found in sheltered rock pools and crevices, one should be
very careful not to put one's hands where they cannot see.
First aid for blue-ringed
The venom contains tetrodotoxin,
which blocks sodium channels and causes motor paralysis and occasionally
respiratory failure. Though with fixed dilated pupils, the senses of the
patients are often intact. The victims are aware but unable to respond.
is a recommended first aid. Prolonged artificial respiration may also be
required. Envenomations may require supportive treatment including mechanical
ventilation until the effects of the envenomation disappear. There is no
antivenom available in Australia.