44 PRESIDENTIAL ADDRESS SECTION C. 



them, would be able to increase with comparatively little molesta- 

 tion. The Red Locust, so far as known, lacks the advantage 

 of possibly indefinite suspension of development in the eg-g 

 state and also of a second generation in one year. These 

 differences from the Brown Locust may account for the Red 

 Locust being a less frequent marauder of the Union, and also 

 for its appearing on the scene a year or two later, but I think 

 it not unreasonable to assume that there are peculiarities in the 

 economy of the Red Locust that compensate to some degree for 

 its longer life cycle and for the limitation of its egg stage. I 

 shall not, however, detain you now with my surmises in this 

 direction. The fact remains that the numbers of both species 

 may increase most extraordinarily in the space of a few years, 

 then fluctuate considerably, and more or less gradually subside 

 until they altogether disappear from the common notice. I 

 think the first rapid increase is accounted for by a comparative 

 inadequacy of natural enemies following a cyclical change in 

 rainfall, but the fluctuations that then occur away from the 

 permanent habitat necessitate further guess work in mv search 

 for a suitable explanation. I find it difficult to conceive that 

 the insects may increase again in their temporary abode once 

 their enemies start their numbers on the downward course unless 

 re-enforcements come from the arid regions. (^ur records of 

 swarm movements indicate that some re-enforcements do come, 

 but the origin of these swarms requires elucidation. I can only 

 conjecture that extensive re-infestation of the relatively desert 

 parts occur from the better watered regions, giving rise to 

 the supplementary invading swarms, or that the checks are much 

 less efficient in the permanent breeding ground, and that therefore 

 the duration of the period of excessive numbers is more pro- 

 longed there. It has been surmised, even stated as a fact ( Trans- 

 vaal Agricultural Journal, July, 1907. p. 951) that the swarms 

 of the Brown Locust bred in the temporary region in spring 

 migrate to the permanent region and breed there in the summer, 

 giving rise to swarms which then seek the temporary region in 

 the fall ; but there is really little definite data indicating instinc- 

 tive return migrations. Reliable observations on the point are 

 sorely needed. At present, I think that the return migrations 

 that occur are due to wind movements and not to inherent 

 inclination. 



It seems quite possible that some of the enemies of locusts 

 are less efficient against the insects in the Kalahari than in the 

 settled parts of the Union, but here again exact observations are 

 much needed. It has been plausibly suggested that, owing to 

 the scarcity of surface water in the so-called desert, the large 

 Locust Birds {Ciconia spp.) are unable to remain, and hence that 

 the locusts there escape in large measure the inroads of these 

 inveterate enemies. 



The enemies of locusts are many and varied in every locust 

 country, and South Africa has its full share. In all countries 



