1928] The Tarsal Chemical Sense of the Screw Worm Fly 201 
THE TARSAL CHEMICAL SENSE OF THE SCREW 
WORM FLY, COCHLIOMYIA MAC ELL ARIA FAB. 
By Cyril E. Abbott, 
Elgin, Illinois. 
In 1921 Minnich found that the tarsi of Pyrameis atalanta 
Linn, and of Vanessa antiopa Linn, are sensitive to certain 
soluble compounds. He (1922) further demonstrated that a 
variety of compounds, when applied to the tarsi, result in an ex- 
tension of the proboscis. Under some conditions even distilled 
water gave this result. The threshold varies with the physio- 
logical state of the animal. In 1926 Minnich also published a 
paper demonstrating that Phormia regina Meigen, P. terrce-novce 
R. D., and Lucilia sericata Meigen also have this tarsal sense. 
These flies distinguish between water, paraffin oil, and saccharose 
solution by means of the tarsi and the oral lobes of the probosces. 
The chemical senses of the screw worm fly ( Cochliomyia 
macellaria Fab.) have been much studied and discussed, but 
owing to the fact that this work has been concerned with purely 
practical results, it has not greatly clarified the problem. (See 
U. S. D. A. Bui. No. 1472). While working for the Bureau of 
Entomology during the summer of 1928, it occurred to me that 
in order to study properly the chemical senses of these insects, 
separation of contact and distance stimuli was necessary. The 
short time at my disposal was accordingly devoted to the de- 
monstration and study of tarsal receptivity. 
Newly emerged flies were constantly available, and these 
were generally used. As these young flies were very restless, it 
was often necessary to defer the tests to the day following emer- 
gence. In no case were flies over twenty-four hours of age used 
in the first series of tests. Each fly was put into a shell vial (2 . 5 
x 10 cm.), the open end of which was then closed with a single 
layer of cheese cloth held in place by a rubber band. Each fly 
was tested by wetting the cloth with the test substance. Ex- 
tension of the proboscis was recorded as a positive response; the 
converse was considered negative. Flies that extended the pro- 
boscis before stepping upon the cloth were marked positive to 
