The defensive spray of a single female of the rare carabid beetle,Helluomorphoides clairvillei (subfamily Carabinae, supertribe Lebiitae, tribe Helluonini). was found to contain a mixture of compounds, including carboxylic acids (formic, acetic), aliphatic esters (principally nonyl acetate), and hydrocarbons (principally decane). In a single series of discharges, the beetle ejected a total of about 1% of its body weight as formic acid (1.1 mg). Our findings demonstrate that characterization of secretory components from even minimal samples of secretion should be possible in many cases.