PRESIDENTIAL ADDRESS — SECTION C. 4I 



of mating couples and spreading out from the sides, the impulse 

 to migrate further in the one case being overcome by the encum- 

 brance of developing ova, and in the other by liberation from 

 the dense mass. The effect is to spread the insects over an 

 area extensive enough to promise ample sustenance for the next 

 generation, when even they themselves might perish through 

 starvation if they were to remain in the region of their origin. 



The chain of reasoning I have followed supposes locusts 

 to be continually present in arid regions, from which occa- 

 sionally they come in swarms ; but, as a matter of fact, almost 

 nothing is known of locusts in the intervals between their periods 

 of abundance. Here is one important point on which reliable 

 observations are necessary before our knowledge of the locust 

 problem can be considered satisfactory, and it is a point which 

 I think might easily be settled in South Africa with respect to 

 the Brown Locust. I am inclined to believe this species to be 

 permanently resident not only in the Kalahari and Bushmanland, 

 but in Griqualand West, the eastern half of the Orange Free 

 State, and northern and central parts of the Cape Province. 

 By permanently resident, I do not mean that I think it common 

 enough to attract casual attention, but that a careful watch 

 would show it to occur in small numbers here and there in 

 localities specially suited to it. It seems to me probable J:hat 

 even in the regions where the greatest swarms develop, it is for 

 years at a time an inconspicuous insect. The present year is 

 not a suitable one for observations on which to base definite 

 conclusions regarding the hal)its of locusts between periods of 

 abundance. This Ijecause, swarms l^eing here and there in the 

 country, it cannot be denied that scattered locusts might possibly 

 be stragglers from swarms that may be imagined to have passed 

 by unobserved. However, after the public was urged by repeated 

 newspaper references to be on the watch, specimens reached the 

 Division of Entomology from a number of points far distant 

 from where any definite swarms were known to have been for 

 years. And, moreover, the locusts in the parts that were most 

 infested occurred principally in loose, open swarms, or clusters 

 of a few score or a few hundreds, or even as scattered indi- 

 viduals or couples. There was a notable scarcity of compact 

 swarms this year, and up to the time of preparing this address 

 <here have been no reports that suggest a migration as distin- 

 guished from local flights. 



The causes that give rise to excessive multiplication are 

 now merely conjectural, and intelligent observation bearing on 

 the explanations that are offered are much needed. It is con- 

 sidered that, during a series of unusually dry years, grasshoppers, 

 and plant-feeding insects generally, come to be held in check 

 more and more by limitation of their food supplies, and less and 

 less by predatory and parasitic enemies. It follows that, when 

 a particularly good season comes along, the plant- feeder gets 

 almost the full advantage of its potentiality for increase, alwavs 



