Consistent behavioural differences have long been recognized in animals but it still remains unclear how these traits change over ontogeny. As individuals can face different situations over their lives, and their life history expectation may not be the same in different life stages, one can expect that using different strategies in different life stages would be advantageous. Characteristics of animal personality across ontogeny could be measured at group and individual levels. Since personality alteration across time can be studied from various aspects one should use the following indexes: mean-level, differential, structural and individual consistency. We investigated whether common firebugs behave in the same way through a major life stage transition, namely final ecdysis. We measured activity, boldness and exploration twice in the larval stage and also twice when bugs reached the adult stage. We found that the relative value of behavioural traits was stable across ontogeny and the correlation structure among behavioural traits remained constant over time. Nevertheless, larvae differed from adults in general in that they were bolder, explored their environment more thoroughly and seemed to be more active before final ecdysis. These results indicate that personality could change differently across major life stage transitions; therefore this important factor needs to be considered in further research.