By using chemical analyses, as well as laboratory and field behavioral tests, we tested the hypothesis that rove beetles of the myrmecophilous genus Pella use alarm pheromone compounds to avert attacks by their host ant Lasius fuliginosus. The secretions of Pellafunestus and P. humeralis contain quinones and different aliphatic compounds, mainly undecane and 6-methyl-5-hepten-2-one (sulcatone). The latter two chemicals are also found in L. fuliginosus pheromone glands. Behavioral tests confirmed that undecane serves as an "aggressive alarm"-inducing pheromone in L. fuliginosus, whereas sulcatone most likely is a "panic-alarm"-inducing pheromone. The main tergal-secretion compounds, various quinones and undecane, individually and in mixtures induced aggression in L. fuliginosus workers. When sulcatone was added to these compounds, the space around the odor source was avoided and a reduced number of aggressive acts observed, suggesting that sulcatone blocks the aggression-inducing effect of undecane and the quinones. These results support the hypothesis that Pella beetles mimic alarm pheromones of their hosts. This is a rare example of chemical mimicry in myrmecophilous insects in which chemicals other than cuticular hydrocarbons are used.