The shell‐boring gastropodOcinebrina edwardsisustains itself by preying on mussels. In the laboratory these drills, when presented with a choice between well fed and starved prey, were attracted to a statistically significant degree (P < 0.01) towards the well fed mussels. Chemical signals, i. e. attractant and/or repellent substances which were being continually emitted by the mussels, informed the predators from a distance as to the physiological condition of their prey. Results of any predation tests which fail to take this aspect into consideration may be biased and tests carried out on animals which have been kept for a long time in captivity are to be avoided.