Most venomous cephalopod
Hapalochlaena lunulata, Hapalochlaena fasciata
0.87 mg 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 tetrodotoxin (TTX). With a subcutaneous LD50 value of as little as 12.5 micrograms (μg) per kg of body weight, for a 70-kg (154-lb) adult human, a dose of just 0.87 mg could prove lethal from a bite. Fortunately, blue-ringed octopuses are not considered aggressive and normally bite only when they are taken out of the water and provoked.

Administered intravenously, the LD50 of TTX is significantly lower: as little as 2 µg/kg could be fatal, equating to a potentially lethal dose of just 0.04 mg for an adult 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.