302 REPORT UNITED STATES ENTOMOLOGICAL COMMISSION. 
In Arizona the fertile area is still farther circumscribed, being not 
more than 3,000 square miles. It is found only on the higher plateaus, 
the Uinkaret, the Paria, and Sand Dime, in the valley of the liio de 
Chelly, and in Nine Mile Valley. 
In Nevada the area is about the same, and is nearly all confined to 
the mountain ranges in the aortheasl and a few valleys on the northern 
border, such as that of Quinn's River. 
It would seem, therefore, that of the 400,000 square miles embraced 
in the Permanent Region, but about 177,000, or about one-third of the 
whole, is of such a character as to permit excessive multiplication of the 
locust. Some 10,000 are contained in Washington Territory, Oregon, 
and Idaho, where the movements of the locusts are neither so regular 
nor controlled by the same laws as are those of the hordes which breed 
in the Northwest, east of the mountains. It is noticeable also that in 
British America there is more land favorable to permanent breeding 
and excessive multiplication than in all the rest of the Permanent Region, 
and that the country in Montana just south of the boundary line fur- 
nishes the next largest amount. 
We will therefore at once consider in how far each of the preventive 
measures is practicable in this plains area, and the results that may be 
expected from liberal government support of either. 
1. Encouragement to settlement. — That every encouragement 
to the settlement of the Northwest should be given we have endeavored 
to show in Chapter II. Aside from the fact now generally conceded, 
and which the experience of the last quarter of a century seems to demon- 
strate, tha t the climate is materially modified and rendered more humid 
by settlement and cultivation, it is also a self-evident fact that in pro- 
portion as the farming population increases and pushes into the region 
where the locust permanently breeds, in that proportion will the extent 
of those permanent breeding grounds be reduced by man's necessary 
efforts in self-protection. 
Compared to the excessive injury from locusts which formerly pre- 
vailed in Central Europe, there has been great freedom from their ravages 
during the past century, a fact evidently due in large part, if not entirely, 
to the increase of population and settlement. With a dense population 
it is easy to adopt preventive measures by destroying the eggs and young 
of invading swarms. So also in Utah the injury and fear of injury on 
the part of the Mormons have decreased in proportion as population and 
settlement increased. 
The belief is very general among those who have studied the subject 
that the planting of tree belts and forests tends greatly to ameliorate a 
dry climate by causing rain precipitation where otherwise the clouds 
would pass over and away, as well as by more nearly equalizing the 
normal annual rainfall, which, on our plains, is generally borne to earth 
in torrential storms, which do comparatively little good. We have no 
doubt but that the belief is well founded, for careful researches carried 
