Stenolemus bituberus Stål is an araneophagic Australian assassin bug (i.e. it preys on web-building spiders). As a step towards more thoroughly understanding the behaviour and predatory biology of this species, here we provide baseline information about development. During its development, there are 5 instars, with the 4th instar being the longest. The length of the 4th instar was consistent with this species' phenology in the field and corresponds to the winter months. Mortality during the 4th instar was higher than in any other instar. Sexes were similar in size until the 5th instar (width across eyes was greater for males than for females, a pattern continued into the adult stage). Overall, adult females tended to be larger than males. The growth rate between instars varied according to instar, although the transition from 5th instar to adult was generally associated with a decrease in growth rate compared with other transitions. Width across the eyes was the only metric that exhibited a sex difference in growth rate, with males growing more than females during the transition from 4th to 5th instar.