1. The stridulation of the scorpions Opisthopthalmus latimanus and O. nitidiceps is described; one of the two mechanisms previously suggested for sound production is shown to contribute almost nothing to the noise. An examination of the responses of a number of small mammals to the stridulation suggests that its biological significance is that of a threat. 2. The caudal stridulation of Parabuthus planicauda is described and it is suggested that it may have arisen from an intention movement of stinging. 3. Reports of stridulation in other genera are examined and it is concluded that the stridulatory movements of scorpions may, in general, be regarded as elaborated from intention movements or displacement activities associated with threat.