Several species of mantids perform defensive displays during close-range encounters with predators. In adult Mantis religiosa, this display entails both visual and acoustic components, the latter being abdominoalary stridulation. Stridulatory modifications of the abdomen and hindwings and acoustic properties of the defensive sounds of M. religiosa are characterized here for the first time. Defensive sounds are generated via an abdominoalary mechanism involving contact between teeth found on the longitudinal veins of the metathoracic wings and pegs located on the abdominal pleura. Defensive stridulation in M. religiosa is highly variable in both spectral and time domains. Inter-individual variability may be stochastically greater than intra-individual variability for at least one acoustic parameter (peak frequency). The loudest portion of a sound emission (syllable), or down-pulse, has an average duration of 195 ms and features an abrupt rise to maximum amplitude. Inter-syllabic intervals are irregular and rate of syllable production depends on a mantid's sex. The acoustic output of M. religiosa is nonresonant, broadband, and of relatively low intensity. A minor ultrasonic component may be present in the spectra of these mantids (particularly in males). The modal peak frequency range (4 kHz interval) is 8-12 kHz (mean range ∼7.4-9.4 kHz). Acoustic parameters which appear to vary between the sexes and/or among females at different reproductive stages, may be related to the sexual size dimorphism of this species and morphological constraints associated with egg-bearing. The acoustic output of M. religiosa is considered with reference to its intended receivers and plausible mechanisms of predator deterrence.