City grasshoppers and country grasshoppers
Grasshoppers from urban (= noisy) areas make more noise to attract females than grasshoppers from more rural, quiet areas. They also do this in a quiet lab environment, which suggests that it is not a temporary, spontaneous adaptation.
Ecologist Ulrike Lampe and her colleagues from Bielefeld University (Germany) collected 188 male bow-winged grasshoppers (Chorthippus biguttulus), a common species in the grasslands of central and northern Europe. Half of the grasshoppers were collected in quiet, more rural areas, and the other half in noisier environments such as those near busy roads. The males were exposed to females of their species and sang their songs of love. This mating song is two seconds long and they ‘sing’ it by rubbing their hind legs against their front wings. The city grasshoppers, but not their country counterparts, amplified their bass tones.
The explanation for this alteration in their song is that the louder bass tones are more audible above the traffic noise that otherwise would disturb the insects’ mating ritual. The fact, say the researchers, that the urban grasshoppers also sing more loudly in the quiet lab indicates it is not a spontaneous adaptation to noise, but a long-term effect.
Earlier research had already demonstrated that human-produced noise influences the calls of birds, whales and frogs. This is the first study to discover a similar effect in insects. Lampe suspects that the effect is not only present at the side of roads, but also in other noisy locations, such as construction zones, airports and train stations. The results of the experiments are described in an article in Functional Ecology.