INSECT MUSICIANS SNODGRASS 



445 



the earth for most of 17 years in immature stages, but there are 

 many broods and each brood has its emergence year independent of 

 the others. In the South there is a 13-year race of this same species. 

 Any large brood of the periodical cicada creates a great disturbance 

 when it issues and the matured adults begin their daily choruses 

 in the trees. The first notes are soft purring sounds, generally heard 

 from individuals sitting low in the bushes, probably those that have 

 but recently emerged from the ground. The next is a longer note, 

 characterized by a rougher or burr sound lasting about five seconds, 

 always with a falling inflection at the end. This song is popularly 

 known as the " Pharaoh " note. Finally, when the swarm is collected 

 in the trees, there is the grand concert of long burr-r-r-r-Wke, notes, 

 repeated all day and day after day till the middle of June, by which 

 time the females have deposited the eggs for the next generation, and 

 the concerts end with the 

 death of the performers. 



The cicadas belong to 

 a different order of in- 

 sects from that of the 

 grasshoppers, ka t y d i d s, 

 and crickets, being mem- 

 bers of the Hemiptera, all 

 of which have sucking in- 

 stead of biting mouth 

 parts. The cicadas, more- 

 over, produce their music 

 by a quite different meth- 

 od from that used by any 

 of the Orthoptera. Just back of the base of each hind wing, in the 

 position of the ear of the grasshopper, there is an oval membrane 

 like the head of a drum set into a solid rim of the body wall. In 

 the periodical cicada the drums are exposed and are easily seen when 

 the wings are lifted (fig. 30, Tin). In most of the other species they 

 are covered by a flap of the body wall. The cicada, however, does 

 not beat his drums; the drum heads are set into vibration by a 

 pair of great muscles attached to them inside the body (fig. 31, A, B, 

 TmMcl). Each drum or tympanum (Tm) is ribbed, the number of 

 ribs varying with different species. 



A membrane or thin sheet of any material which produces a sound 

 by vibrating must have air of equal pressure on both sides of it 

 and air free to respond to any changes of pressure. The drum head 

 of the cicada thus could produce no sound if its inner face were in 

 contact with the viscera or blood of the body cavity, and between 

 the two tympana there is actually a great air cavity which extends 

 1454—25 30 



Fig. 30. — A male of the 17-year cicada (TiMcina 

 septendecim) , with wings elevated to show the 

 sound-producing drums or tympana (Tm) on the 

 sides of the first abdominal segment 



