PKEVALENCE OF LOCUSTS IN DRY REGIONS. 55 
or vast treeless areas, and an arid or dry climate. The desert character 
of that vast region of Northern Africa extending from Senegal to the 
Mediterranean, and from the Atlantic to the Eed Sea, is well known, as 
is also the arid and desert character of a large part of Arabia, Syria, 
Persia, and Mesopotamia. The Ukraine, Crimea, and the regions around 
the north and east of the Caspian Sea, are characterized by those broad, 
treeless, and more or less elevated plains to which the name steppes has 
been applied. Extensive pampas and treeless plains form a marked 
feature of those sections of South America in which the locusts are 
found. The same we know also to be true in reference to the locust 
districts in North America. Keferstein remarks 148 that high chains of 
mountains covered with snow are the best natural barriers against the 
extension and migrations of the destructive locusts. That this may be 
true when applied to some species is not to be doubted, but that it is 
applicable to all is disputed by the history of our native species, C. spretus. 
Eitter assures us 149 that no traces of locusts are found in the cold climate 
of Thibet, in cool Cashmere, and that in the central interior of Asia, be- 
tween the Himalaya and Altai mountain systems, and on the plains of 
Dekkan, in the south of Nerbudda, or in India beyond the Ganges, be- 
tween the Brahmapootra and Irawaddy Eivers and Tangtse-Kiang, 
where a misty, rainy, maritime climate prevails, the locust plague is un- 
known. 150 
Judging from the silence of Stanley, Schweinfurt, and some other recent 
travelers in reference to locusts, there is a large region in Central Africa 
in which they do not prevail. The same appears to be true in regard to 
a large part of the northern portion of South America, where a rich and 
luxuriant growth of vegetation and a moist climate prevail. The free- 
dom of Eastern North American from this pest is well known. 
A third important conclusion to be drawn from our brief review is 
that locust migrations are not governed by any law of regular peri- 
odicity. If we divide the number of years given by the Chinese rec- 
ord (1,924) by the number of visitations (173) it gives an average of 
a little over 11 years. The time embraced in Koerte's list of the 30 inva- 
sions of Germany also gives an average of a little over 11 years. Kop- 
pen'slistof the visitations of Eussia and adjoining regions 151 from 1008 to 
1861 gives an average interim of something over 13 years. Although 
the average periods thus obtained by dividing the whole number of 
years by the number of visitations agree so nearly, yet by simply run- 
ning the eye over the lists of years any one can see that this argument 
is purely accidental and will not hold good when applied to the various 
interims. In the earlier times less attention was paid not only to the 
study of natural history but to agriculture than at present, and only the 
Mag., May, 1878, quoted in our former Report, p. 477, 
1,000 feet in Altyn-Tag range, in Central Asia. 
'«L.c. 
,43 neusclireckenplage der Alten Welt, p. 7. 
150 But see statement of Colonel Frejvalsky, Geo2 
that swarms of locusts were seen at an elevatioi •' 
161 " Heuschrecken in Siidrussland," pp. 110-12. 
