
Saturday, March 21, 2009
23b

Tuesday, March 17, 2009
Chaminuka 2.0



On the job
science week


"It is well known that ants do not respond to sound on a human scale. You can shout at an ant and it doesn't seem to notice. Yet many ant species communicate by means of squeaking sounds from a stridulatory organ on the ant's body, consisting of a washboard-like set of ridges and a scraper. The squeaking sounds are usually very faint but they pervade ant colonies. Sounds from individual ants can be heard distinctly and there are a number of different signals. The sounds are in the audible frequency range around 1kHz. Because ants appear to be deaf to airborne sound on a human scale, myrmecologists have inferred that they transmit stridulation signals through the soil, or other solid substrate. For a number of reasons, however, this mode of transmission is highly unlikely. A more likely explanation is that ants communicate with each other through the air using nearfield sound. As with other insects, ants are believed to "hear" airborne sound with their antennae, using hair-like sensors at the tips. By sensing the relative difference in sound displacement between the tips of the antennae, an ant can detect a stridulation signal in the nearfield, where displacement changes rapidly with distance, but can not detect sound in the farfield, where displacement changes more gradually. This explains how ants can detect sound from other ants while, at the same time, being unaware of sound on a human scale. This is fortunate for ants because they would otherwise be overwhelmed by background noise, both natural and man-made."

Sunday, March 1, 2009
Lake Kariba





swimming


