66 PLANT-BUGS INJURIOUS TO COTTON BOLLS. 
and one-half millimeters long, shortly after being brought into the 
laboratory from a cotton field, killed and partially ate a first-instar 
nymph of a Pentatomid of the genus Thyanta. 
Attacking adults. — No invertebrates are known to attack adult con- 
chuelas, nor has the writer found any reference on this point in the 
case of other Pentatomids. Broken and empty shells of adults have 
been found in cotton fields in midsummer, but there is no direct evi- 
dence to show this to be the work of predatory enemies, although it 
may be suspected. 
BIRDS. 
In spite of much evidence to the contrary, scattered in various 
scientific publications, it is the prevalent idea that the offensive 
odor of bugs protects them from birds. Without this supposition 
the object and origin of the odoriferous glands may be difficult to 
explain, but studies in the feeding habits of insectivorous birds has 
shown that in most cases Pentatomid bugs are eaten at least to the 
extent of the proportion of their numbers to the numbers of other 
insects of the same and larger size. Further, it would seem that 
some birds, like the crow, possess a predilection for insects of pungent 
or otherwise strong taste or odor. Careful studies have been made 
of the feeding habits of about 20 common American birds. Almost 
without exception Pentatomids (variously referred to as u stink 
bugs," "soldier bugs," and ''Pentatomids") are included in the diet 
of each of these birds, amounting on the average to about 3 per cent 
of all the food. 
Thus far no specific observations have been made for the purpose 
of determining the extent to which birds feed upon the conchuela. 
It is evident, however, that there is some important influence com- 
bined with egg parasitism to produce in midsummer the marked 
reduction in number of these insects observed both in Mexico and in 
Texas. The egg-parasites effectually check the multiplication of the 
pest after the month of July, but the diminution in numbers of the 
adults remains unexplained. In the laboratory, protected from their 
enemies, the life of the adult conchuela extends over many weeks, 
27 specimens collected at Tlahualilo between July 6 and July 10 
averaging over two months each. 
It is inconceivable that the difference between field and laboratory 
conditions should be so great that, of the insects of the field on July 
10, over 60 per cent should die from natural causes before August 1, 
while in the laboratory less than 5 per cent should die during the 
same period. Furthermore, if the numerical decrease in question 
had been due to natural exhaustion of vitality of the adult insects, it 
would be expected that many dead specimens would have been 
found in the cotton fields. As a matter of fact, dead specimens were 
exceedingly rare and the few found gave evidence of having been 
