We report the identification of a defensive secretion from the green lacewing, Chrysoperla carnea. By using combined gas chromatography-electroantennographic detection (GC-EAD), we found one major compound in the solvent extract of this secretion that elicited a significant EAD response from the antenna. Based upon its characteristic fragments from gas chromatography-mass spectrometry (GC-MS) analysis, the compound was identified as a tridecene. Dimethyldisulfide derivatization suggested that a double bond was located between positions 4 and 5 in the carbon chain. Thus, the compound was tentatively identified as a 4-tridecene. Coinjection of the extract with a mixture of the Z or E form of the synthetic 4-tridecene revealed that the unknown was (Z)-4-tridecene. EAG dose-responses showed a direct correlation to dose. Single sensillum recordings from sensilla trichodea situated on the antennae suggested the presence of receptor neurons specifically responding to this compound. An arrestment behavior was observed when tested in the Y-tube olfactometer. Preliminary field trapping results indicate that the compound is an antagonist to attraction. The avoidance behavior of predatory ants, observed when tested with the synthetic compound of this secretion further suggested a defensive function.