The Bulletin 
111 
soil to a depth of from four to five inches. In those cages that were 
left undisturbed the mortality was usually only about 10 per cent. A 
single disturbance of the beetles seemed to increase the mortality very 
much, and in cages where the beetles were disturbed several times they 
all died. 
In the fields careful counts of plats averaging about one-third acre 
show that normally the numbers decrease from a rate of about 1,250 
per acre in July of one season to about 420 per acre by the end of May 
the following season, by which time it is believed all of the adults have 
emerged from hibernation. This would give a mortality of about 66 
per cent, provided all the beetles returned to the same fields; but, as 
pointed out in another connection, we have not been able to prove that 
any of the beetles returned to the same fields in which they worked 
the previous season, although, in spite of our negative evidence, some 
beetles undoubtedly do return to the same fields. 
NATURAL ENEMIES 
The corn bill bug is singularly devoid of natural enemies in all its 
stages. So far in these investigations no parasitic enemies of any of 
the stages of the bill bug have been discovered, and only a very few 
predaceous enemies. In the corn-fields in the eastern part of the State 
adults and larvae or various species of ground beetles, lampyrid beetles, 
digger wasps, robber flies, and other predaceous insects, abound. Va¬ 
rious species and individuals of these predaceous insects have been 
watched often for considerable periods. There is no indication that these 
insects prey upon any of the stages of the corn bill bug. Even when 
eggs, larvae, and pupae were exposed directly in the path of these pre¬ 
daceous insects they made no effort to devour them. 
The little brown corn-field ant is also constantly present in the fields, 
and these have frequently been observed with eggs of the corn bill bug 
in their jaws, evidently having picked up eggs that were carelessly 
deposited or that had been deposited in the ground among the roots. 
There is no evidence that this ant enters the egg cavities and removes 
eggs that have been carefully deposited, although they are constantly 
running up and down the stems of corn plants, especially corn plants 
infested with root lice. In fact, the eggs are for the most part so well 
placed that it is rather doubtful whether ants would be able to secure 
any carefully placed eggs. However, ants have been seen with eggs so 
frequently in the field that one is led to suspect that they destroy a 
great many eggs in this way. Mr. Smith well says (Smith, 1913) : 
“An egg dropped or placed on the ground or exposed on the plants is 
very quickly taken away by the little field ants. Just how much benefit 
they cause by destroying the eggs the writer has not had a chance to 
discover.” 
In October, 1915, I chanced upon the following observation, which is 
given in some detail because insect enemies of the corn bill bug are so 
8 
