Ants in four subfamilies stridulate, but others seem silent and don't have recognizable scraping surfaces, Ward notes. Entomologists argue about whether this pattern means stridulation evolved several times in ants or whether the Adam and Eve of ant ancestors rasped to each other but some descendants lost the ability. In the 1970s, pioneering studies of these ant scratchings showed that they boosted the listening ants' response to the pheromone signals indicating that dinner or a nest site is available. Nestmates too small to manage any heavy cutting get a free trip back to the nest. They aren't just useless weight since they reduce the risk of attack by phorid flies.
Hitchhikers find rides in part by vibrations from the stridulation noises the cutters make.
Stridulation also seems to summon rescuers after a nest cave-in. If the workers were buried only 3 cm below ground, nestmates not only milled around the spot but dug toward the pinned ants. One of the more unusual notions about stridulation arose in 1995 when Flavio Roces and Bert H lldobler of the University of W rzburg in Germany reported that leaf-cutting ants tend to stridulate as they slice off snippets of tender leaves. However, offering ants both prime leaves and chemically tainted ones revealed that workers stridulate more on desirable than less-favored leaves, regardless of any differences in the toughness of the cutting task. Buzzing jaws do make smoother cuts, the researchers found, but don't improve speed or efficiency.