 Male mole crickets sing by <unk> , always underground . In Gryllotalpa gryllotalpa the song is based on an almost pure tone at 3 @.@ 5 <unk> , loud enough to make the ground vibrate 20 cm all round the burrow ; in fact the song is unique in each species . In Gryllotalpa gryllotalpa the burrow is somewhat roughly sculpted ; in Gryllotalpa vineae , the burrow is smooth and carefully shaped , with no irregularities larger than 1 millimetre . In both species the burrow takes the form of a double exponential horn with twin openings at the soil surface ; at the other end there is a <unk> , then a <unk> bulb , and then an escape tunnel . A burrow is used for at least a week . The male positions himself head down with his head in the bulb , his tail near the fork in the tunnel . 
