26 THE CHINCH BUG. 
GREGARIOUS HABITS OF THE CHINCH BUG. 
I Lave previously called attention to the gregarious habits of the 
chinch bug, and only refer to the phenomenon again because it is to 
this that its destructiveness is largely due. It is not because of the 
excessive numbers, but the persistency with which they will congregate 
en masse on limited areas, that renders their attacks so fruitful of 
injury. With an ample supply of food the young develop and leisurely 
diffuse themselves over the adjacent fields, and there are neither 
swarming flights nor migrations. In 1884, in northern Indiana, a small 
field of wheat was severely attacked by chinch bugs. At harvest 
there was every prospect of a migration from the field of wheat to an 
adjacent one of corn, and the bugs were present in sufficient numbers 
to have worked serious injury to the latter; but the wheat had grown 
up thinly on the ground, and there had sprung up among the grain a 
great deal of meadow foxtail grass, ISetaria glauca Beauv., and panic 
grass, Panicum crus-galli L., and to these grasses the bugs transferred 
their attention, finishing their development thereon, and later, so far as 
I could determine, they scattered by flight out over the adjacent fields, 
working no further injury. Pedestrian migrations may continue for a 
fourth of a mile or even more, but on reaching a suitable food supply 
the tendency is to congregate upon their food plants until these are 
literally covered with chinch bugs, varying in color from the black and 
white adults to those of the more advanced larvte. (See Fig. 5). What- 
ever tendency there is exhibited toward a wider diffusion is confined to 
the adults, the others remaining and leaving in a body only when the 
plant on which they have congregated has been drained of its juices and 
has begun to wither, when they simply crawl to the nearest plants and 
again congregate upon them as before. In case the migration has been 
to a field of corn, and if this is badly overgrown with either of the two 
grasses previously named, the bugs will collect upon the latter, and 
unless the corn plants are very small they will not as a rule attack them 
until the grass has been killed. Some farmers have gone so far as to 
claim a benefit to be derived from a certain abundance of chinch bugs, 
the statement being made that they will kill out these grasses to an 
extent that nothing else will. It is clear that the acquisition of wings is 
not the signal for the adults to abandon the companionship of the larvae 
and pupae, yet they do gradually disappear from among them. It is 
possible that the disposition to pair does not exist until the individual 
has reached a certain age beyond seeming maturity, and that it is not 
until the passion for mating has overcome their gregarious inclination 
that they are disposed to migrate. Or it may be that the phenomenon 
may be explained on the supposition that when the pairing season 
approaches the males scatter out in order to find females with which 
they are not akin, thus following out natural selection and preventing 
a continual interbreeding. Over the northern United States, at least, 
