Although it is well known that ants generate sound by stridulation using gaster-flagging motion of the abdomen, acoustic communication by ants is generally believed to be almost nonexistent compared to chemical communication using pheromones [Holldabler and Wilson, The Ants (Harvard U. P., Cambridge, MA, 1990), pp. 255--259]. Contrary to this prevailing belief, it has been found that imported fire ants can use acoustic signals for meaningful communication. Signals have been recorded in situations such as alarm, distress, and attacking prey and also what appears to be an all's-well signal. These were analyzed and distinct time-modulation differences were found depending on the situation. Acoustic signals appear to be used for urgent communication. Ant response provides an indication of the significance of the signals. The frequency range is principally below about 2 kHz. The sound-pressure level of a general alarm signal was found to be approximately 40 dB (A), which is about three times the level of a faint whisper. Background noise inside an ant mound is low and interior tunnels can act as waveguides.