LOCUST PLAGUE—UVAROV 339 
curiosity to ask the question, but, fortunately, scientists are often at- 
tracted by “useless” problems. In this case, entomologists in Russia 
and in South Africa undertook investigations, and almost simultane- 
ously, and quite independently, arrived at wholly unexpected, but 
closely similar conclusions. It was found that locusts in the years 
when they are not numerous differ from the swarm locusts in appear- 
ance and in habits. The external differences between the swarming 
and the solitary phases of locusts, as they came to be known, are some- 
times so pronounced that the two phases were considered by specialists 
as belonging to different species. As regards habits, locusts of the 
solitary phase are typical grasshoppers, showing no inclination to 
form dense bands and swarms. Should, however, the numbers of 
locusts in a restricted area increase, so that crowding results, the 
locusts acquire strong gregarious tendencies. The phenomenon of 
phase variation in locusts has since been subjected to intensive studies, 
and many interesting details have been discovered, but the point of 
outstanding practical importance was that it opened up a possible 
approach to the problem of the origin of locust outbreaks. 
NEW PERIOD OF INVESTIGATIONS 
In 1928, a serious outbreak of the desert locust started to develop, and 
the British Government decided that steps should be taken to con- 
sider not only defensive measures, but also the possibility of a radical 
solution of the problem by ascertaining the reasons for the periodical 
swarming of locusts, with a view to their control. A Locust Sub- 
Committee of the Committee of Civil Research (later transformed 
into the Committee on Locust Control of the Economic Advisory 
Council) was formed on April 29, 1929, and that date may be taken 
as the threshold of a new anti-locust policy. The actual work was 
entrusted to a special research unit, under the supervision of Sir Guy 
A. K. Marshall, then Director of the Imperial Institute of Entomol- 
ogy, and under the technical direction of the present writer. A 
scheme for collecting current information on locust movements and 
breeding in all countries of Africa and the Middle East was intro- 
duced, and several field investigators were sent out to study the prob- 
lem on the spot. The organization, set up as a purely British one, 
rapidly attracted attention in other countries, and the First Inter- 
national Locust Conference at Rome in 1930 requested the British 
organization to act as the International Centre for Anti-Locust Re- 
‘search, where all the information on the subject could be centralized. 
The years 1930-38 witnessed a unique concentration of scientific effort 
on locust investigations. Parties of British, French, Belgian, South 
African, Indian, and Egyptian experts systematically explored one 
area after another; spending months in the regions which are rightly 
