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Vol. XXXIX. LONDON, JULY, 1907. No. 7. 



THE STRIDULATION OF THE SNOWY TREE-CRICKET 



(CECANTHUS NIVEUS). 



BY A. FRANKLIN SHULL, ANN ARBOR, MICH. 



L — Introduction.* 



Dolbear (1897), in writing of the chirping of a common cricket, wiiich 

 was probably the Snowy Tree-cricket {(Ecanthus nivetis), described the 

 regularity of rate as "astonishing, for one may hear all the crickets in a 

 field chirping synchronously, keeping time as if led by the wand of a 

 conductor." In an adjoining field, he said, the rate was the same, but the 

 beat was different; that is, the notes did not occur at the same instant. 

 He expressed the relation of the rate to the temperature by the formula 

 T — 50 + ^^ ~ ^" , where T is the temperature Fahrenheit, and N is the 

 number of chirps per minute. For convenience, the formula may be 

 reduced to T = 40 + -. Dolbear does not say that the cricket referred 

 to is CEcaiithtis niveus, though he has generally been so interpreted. 

 Folsom (1906) conjectures that he refers to a species of Gryllus, but I see 

 no reason for this assumption, except Dolbear's mention of daytime cliirps, 

 which are comparatively rare with CEcantkus niveus. It seems more 

 probable, as Edes (1899) suggests, that the cricket found chirping in the 

 daytime was another species which Dolbear confused with CEcantkus. 

 Certainly his formula and statements agree more closely with CEcantkus 

 niveus than with any species of Gryllus. 



Carl A. and Edward A. Bessey (1898) derived from observations 

 made on CEcantkus niveus previous to the publication of Dolbear's paper 

 the formula T = 60 + ^'~''% which dithers notably from Dolbear"s in 

 making the increase of rate 4.7 instead of 4 per degree rise in temperature. 

 They stated, moreover, that below 60 the rate was higher than would be 

 expected from the formula, thus making it evident that the curve of 

 temperature could not be represented by a linear equation. 



Edes (1899) found that while all the individuals of CEcantkus niveus 

 performed in the same tempo, yet the chirps did not occur at the same 

 instant. Using some observations of his own and those of Walter Faxon, 

 he tested Dolbear's formula, and found that the increase of 4 per degree 

 in the rate was nearly correct, but the different sets of data disagreed in 



*Contribution from the Zoological Laboratory of the University of Michigan. 



