As an adult, it can grow up to 20 centimetres (8 in) long (top of the mantle to the tip of the arms) and on average weighs 26 grams (0.9 oz).

These octopuses have an average of about 60 rings that have multilayer reflectors that allow them to flash a blue green color.

[2] This method of muscle contraction and relaxation has not been seen in other illuminating animals (Mäthger et al.)[2] Like other species of the blue-ringed octopus, this variety is named for the vibrant blue rings that it displays when agitated.

[3] Southern blue-ringed octopuses tend to be passive and relatively harmless: they generally use their toxins only when hunting or provoked.

The prey of H. maculosa consists mostly of lobsters, crabs, shrimp, and shellfish, as well as the occasional small fish.

The mating ritual of H. maculosa usually begins with the female initiating reproduction by changing color and posture.

For this type of octopus, there is approximately a two-month window in which a female acquires and stores sperm from multiple males.

The young begin hunting around one month of age- they are said to be venomous from birth, while their blue rings do not appear until six weeks after hatching.

[5] Same-sex attempts at mating were frequently noted, which implies distinguishing between male and female is difficult even for the octopus.

[8] Researchers have been interested in this topic specifically because the female can only reproduce once in her lifetime and because she can store the sperm of her many mates (Oceana).

[8] In the paper, Mating Behavior and Postcopulatory Fertilization Patterns in the Southern Blue-Ringed Octopus Hapalochlaena Maculosa, the authors study did not find that females choose the male sperm that will fertilize their eggs, though the "male that obtained less paternity than expected was in fact the female's full-sibling brother (Morse et al.)."

[10] The neurotoxin, tetrodotoxin (TTX), is secreted in the posterior salivary gland, which is located in the intestinal blood system of the octopus.

Various references in popular culture depict the southern blue-ringed octopus as a nefarious seadevil lying in wait to attack humans with its deadly toxins.

It is also suggested that because the dispersal ability of H. maculosa is limited, connectivity between different populations of the species is especially vulnerable to habitat fragmentation or geographic barriers.