Most venomous cephalopod
Hapalochlaena lunulata, Hapalochlaena fasciata
5.6-9.8 micrograms ranked #1
Not Applicable ()

The two closely related species of blue-ringed octopus, Hapalochlaena maculosa and H. lunulata, native to shallow waters around the coast of Australia and parts of south-east Asia, carry a neurotoxic venom called tetradotoxin (TTX). With an extrapolated LD50 value of 80–140 nanograms per kg, for an average 70-kg (154-lb) human, a dose of just 5.6 to 9.8 micrograms (µg) could prove lethal. Fortunately, blue-ringed octopuses are not considered aggressive and normally bite only when they are taken out of the water and provoked.

It is common for individuals of these two species to contain a total of 7.66 µg of TTX in just their salivary glands – theoretically an ample amount to kill a human.

These cephalopods are fairly small in size, their tentacles having a radial spread of just 10–20 cm (4–8 in).

The term LD50 represents the dose of venom that proves lethal to 50% of a test population, often applied to mice which are the most common test subjects in this field.