STUDIES OF THE OYSTER DRILL 
97 
drop in temperature. The actively drilling animal would stop, leave its victim, and 
move to some other part of the aquarium. Two sets of data in support of this 
are available. On August 26 a sudden drop to 20.0° C. occurred (see temperature 
chart, fig. 5), and the drills that were actively feeding stopped and moved from the 
oysters. Again, on September 20, 14 drills were observed feeding on oysters. At 
this time the water temperature in the laboratory was approximately 27° C. On 
September 24 the water temperature suddenly dropped to about 20° C. and imme- 
diately feeding stopped. Again the drills left their oysters and moved away. These 
same results were obtained in Beaufort. At temperatures below approximately 
15° C. feeding ceased, while sudden falls in temperatures during the summer months 
were equally effective in bringing about a cessation of the drilling activity. 
between 12.30 and 1 p. m. 
From the above observations it seems probable that whenever the temperature 
falls below 10° C. Urosalpinx cinerea becomes inactive, and that feeding does not take 
place at temperatures below 15° C. Even at temperatures above 20° C. sudden 
drops will interrupt the drilling activity. Spawning takes place when the water 
temperature has reached 20° C. 
FEEDING HABITS 
The damage done by Urosalpinx has never been accurately determined for 
oysters beyond the spat age. Rowe (1894) estimated that in southern New England 
the loss was approximately $1,000,000 yearly, and Nelson (1922, 1923) stated that in 
Delaware Bay the drill lolled as many as 50 per cent of 2-month-old oyster spat. 
Galtsoff (1925) estimated that in East Haven River (Long Island Sound) 50 per cent 
of the young oysters had been killed by the drills. In order to get some quantitative 
data on the actual amount of damage done by this pest to large oysters, surveys 
