Abstract The attack of the mantid Stagmatoptera biocellata on prey and the defensive responses elicited when this insect is faced with a bird are analysed during all instars. The static component of the strike keeps a constant relationship with the foreleg extension throughout post-embryonic development. The dynamic component seems to keep one fixed relationship with the foreleg length during the first, second, third, fourth, and fifth instars, and another constant relationship during the sixth, seventh, and adult instars. Two defensive systems are shown, i.e. the cryptic reaction and the deimatic reaction. The former is the sole defensive device in the first and second instars; the latter is the sole defensive device in the adult instar. During instars 3, 4, 5, 6, and 7 larvae display both reactions. The finding that adults of this species do not present cryptic reactions contrasts with descriptions in mantids of other species. The possible cause of this difference is discussed. The elicitation of the deimatic reaction with a given frequency and the choice between both defensive systems seems to depend on the mantid-foe distance. The general conclusion of the paper is that attack and defence are distance-dependent behaviours in all the instars, but that there is a characteristic distance for each instar that seems to keep a certain relationship with the body size of the insect.