Ants are deaf

Workers of a number of ant species produce vibrational signals, a phenomeno n called "stridulation," with a specialized organ located on their gasters. Even though stridulation can be heard by humans as faint air-borne sound, it has repeatedly been shown that ants are insensitive to the air-borne com ponents of such signals. Instead, they are highly responsive to their subst rate-borne components. Contrary to this view, it has recently been claimed that fire ants can hear stridulatory signals produced by nest mates as near -field sound, and that there is no evidence of signal transmission through the substrate in ants: In the present letter, this view is challenged by ca lculating the amplitude of the near-field particle oscillation around a str idulating ant and by comparing it with the sensitivity threshold of the ant sensory receptors. The amplitude is shown to be at least 50 times lower th an the sensitivity threshold, a fact that precludes the perception of the s ignals with the stiff antennal sensilla (and Johnston organ) so far describ ed for ants. Finally, published data and our own findings on vibrational co mmunication in ants are summarized, clearly showing that they are highly re sponsive to the substrate-borne components of stridulatory signals, and ins ensitive to near-field sound. (C) 2001 Acoustical Society of America.