798 REPORT— 1900. 



7. The Locust Plague and its Suppression. By M. MunRo, M.D. 



Locusts Lave devastated the greater part of the habitable world, and during 

 the last ten years have done great damage in the southern republics of South 

 America, in North and South Africa, in India, &c.— countries widely separated 

 from each other — and they have caused great loss of human and anfmal life in 

 large areas in Africa belonging to Britain. The importance of the subject is 

 therefore considerable. But the difficulties which hitherto have been connected 

 with the plague seemed excessive and insuperable barriers in dealing with it 

 eH'ectually. 



To illustrate the remarks in this paper I select the four following typical and 

 well-Iinown species of the insect, namely, 1, the Caloptenus spretus, or Roclvv 

 Mountain locust ; 2, the Stauronotus criatus, or Cyprian locust ; 3, the 

 >Sc/iistocerca paranensis ; and 4, the Acridium perenrinum, or Old World locust, 

 in order to emphasise in a more pointed way certain aspects or characteristics of 

 the insect which I think it well to put prominently forward in attempting to bring 

 this plague under review, and askirg favourable attention as to the best means to 

 check it and alleviate the distress. 



a. Our increased and gradually accumulating knowledge of the habits of the 

 insects is derived mainly while the insects come to and snjourn in their temporary 

 homes, for we do rot yet know them in their permanent or true homes." The 

 one and only success in combating the plague by human means in the whole 

 history of the world was due to the putting in force the simple observation that the 

 young (or the old) locusts cannot adhere to smooth surfaces, such as glass, owing to 

 the fact which is now made abundantly clear, name!}', that, unlike Hies, the pro- 

 cesses or claws on the feet of their front and middle pair of legs are too short and 

 weak to enable them to do this. 



h. The general and characteristic features of the locust run through all the 

 .species alike. This fact has been greatly lost sight of or minimised, and the dif- 

 ferentiations which help to mark off one species from another have been magnified 

 into an unjustifiable and unnecessary importance. The instincts and the structure 

 of all the varieties are very nearly alike, although one species may not be so larga 

 or have different markings as compared with anotlier. 



c. The direction which the ' army ' assumes when the Larvre at a certain 

 period set out for and continue on their ' march ' is a most important matter to 

 settle and be certain about, as this is the most destructive period in the life of the 

 insect. They then devour everything that comes in their way. Not so with the 

 Hight of flying locusts, which only levy toll here and there as they pass or sojourn. 

 The ' army on the march ' usually pursue a straight given course, irrespective of all 

 obstacles and dangers (natural or artificial) that may be in their way, minus any 

 with smooth surfaces owing to tlie reason above stated. Now the course or 

 direction of the ' march ' will be found (though further observation is requisite to 

 confirm the truth fully) to be always in a given direction in certain countries. 

 Thus in the Argentine and South Africa they travel southwards, in Algeria north- 

 wards, in the United States eastwards, and so on. It may not be true south, or true 

 north, or true east in the respective instances mentioned, but it will be respectively 

 toicards the south, north, or east, as the case may be. The important thing to bear 

 in mind h that they all march in one general direction as a body at the same time, 

 and without any leader ; while so far as suitability and abundancs of food are con- 

 cerned to satisfy all their instincts an exactly opposite or other direction would be 

 far better. The ' Screen and Trap ' or ' Cypriote ' system was based on the suppo- 

 sition that the insects march in a given specific direction. It has been owing to this 

 fact that the power of the plague was iDroken in the course of one year (1883) in 

 Cyprus, although it baffled all efforts to check it for centuries before. Since the 

 suppression of the plague, and no doubt very much on account of it, Cyprus has 

 entered on a new era of prosperity. 



Outline of the Means for Checking or Suppi-essinff the Plagve, 

 There is a sense in which a plague or pest such as that of locusts may be re- 

 garded as the increase over the natural checks with regard to the normal number. 



