140 ILLINOIS STATE ACADEMY OF SCIENCE 



SUMMARY OF THE PAPER ENTITLED 



"A METRICAL STUDY OF A THOUSAND MOTH 

 COCOONS." 



Prof. Elliot R. Downing, University of Chicago 



In the autumn of 1916, the cocoons of the Cecropia and 

 Polyphemus moths were very numerous in the southwestern 

 portion of Chicago. Two hundred forty-eight Cecropia 

 cocoons were counted on one small catalpa tree on a lawn 

 in Roseland. A small hickory about two feet high, found 

 growing on the open prairie near the city limits, was so 

 plastered with cocoons that no stem or branch was visible. 



There were two centers of abundance; one in Roseland; 

 the other in the neighborhood of the B. & O. railroad cros- 

 sing at 91st street. These centers had apparently been 

 populated by the moths from a common point in the neigh- 

 borhood of Chicago Heights where the moths had been es- 

 pecially abundant the preceding year. The direction of mi- 

 gration from this original center had been determined ap- 

 parently by the prevailing winds. 



In the fall of 1916, some eighteen hundred Polyphemus 

 cocoons and forty-two hundred Cecropia cocoons were col- 

 lected in the two regions mentioned. Since then, collections 

 have been made annually for the purpose of comparison with 

 the first lot. In 1916, five hundred cocoons each of the Cec- 

 ropia and Polyphemus were taken at random from the 

 thousands collected to make a careful study of the cocoons 

 and moths that were hatched from them. Similar samplings 

 have been made each succeeding year, though in decreasing 

 numbers since the cocoons are becoming scarce. The results 

 of the study may be briefly stated as follows : 



1st — The percentage of parasitized and diseased pupae 

 has increased steadily during this period of five years, un- 

 til now, the season of 1920-21, it is next to impossible to 

 find a viable cocoon. In 1916, about one per cent of the 



