When stimulated with ultrasound, flying mantids perform a multi-component evasion behavior that causes a steep power dive. The maneuver protects them from capture by bats. Did the evasion behavior evolve de novo, was it co-opted from another function that was therefore lost, or is it simply an already existing behavior performed in a different context? A survey of ultrasound-triggered evasion behaviors in 30 species of mantis compared to several defensive behaviors produced in other contexts reveals a very limited repertoire of component movements common to all of the behaviors. The components include prothoracic leg extension, head turn, abdomen dorsiflexion, and wing elevation. Context determines which combination of components is performed and the most effective stimuli. Flight and tarsal contact are major contextual cues. Tarsal contact eliminates sound as an effective stimulus, but does not alter auditory signaling in the CNS. Vibratory stimulation, however, reduces auditory responses. Headless mantids perform coordinated non-flight defensive displays, so the controlling neural circuitry must reside in the thorax. However, headless mantids do not perform in-flight evasive behavior, which has the same components, implying a context-specific 'switch' located in the brain. Our data suggest that there is a single underlying defense system in mantids whose expression is modulated by context. The evolution of specific defensive behaviors probably did not involve major changes in CNS circuitry, but rather alterations in sensory connections to existing behavioral modules.