308 OAS. J. SIMPSON— ENTOMOLOGICAL 



In many places throughout the Protectorate, there are extensive swamps and 

 marshes, which are almost invariably connected with a heavy clay soil. During 

 the rainy season, these may be covered with water several feet deep, but at the 

 height of the dry season, elephant grass, attaining a height of 8-14 feet, 

 generally covers these " fadamas," as they are termed locally. 



This, then, may serve to give a general idea of the main types of vegetation 

 occurring in Northern Nigeria, and in this connection it might be well to 

 remember that when any type of tropical vegetation is devastated, it is generally 

 replaced by a drier form, and this again, if demolished, will give way to a type 

 of vegetation unlike its predecessor, but always diminishing in density and 

 consequent shade and surface moisture. 



II. Climate and Rainfall. 



Having discussed the general physical configiu-ation of the Protectorate, we 

 we may briefly review the main climatic conditions which obtain in the different 

 regions, and so form a definite basis for a study of insect distribution. In this 

 way many points, otherwise obscure, in connection with the limits of the various 

 species of Glossina and other blood-sucking flies, will be more easily grasped, as 

 there can be little doubt that the relative duration of the wet and dry seasons, 

 the varying degrees of humidity, and the annual range of temperature have a 

 distinct bearing on this subject. 



No review of the meteorology of Northern Nigeria has been published, nor 

 has any attempt been made to consider the extremes of climatic conditions to be 

 found in the Protectorate. The following observations, therefore, are based on a 

 study of the raw meteorological data compiled during recent years at the various 

 stations, published in the oflScial Gazette, and supplied to the Meteorological 

 Office. In order to avoid a lengthy discussion on this subject, several tables have 

 been prepared, so that a glance at these will bring out in a more concrete form 

 much of what follows. 



Northern Nigeria, as has already been pointed out, lies roughly between the 

 7th and the I4tli parallels, and the climate is therefore tropical but not equatorial. 

 By this is meant that in contrast, for example, with Southern Nigeria, the 

 rainfall and temperature curves show only one annual maximum and minimum. 

 In the latter colony, except in the north-west corner, which is geographically in 

 Northern Nigeria, the temperature curve reaches its highest maximum in March 

 and April, after which it descends, but again reaches a secondary maximum in 

 September and October. The curve of rainfall shows similar maxima and 

 minima. 



The prevailing wind in Northern Nigeria is the Harmattan, a dry hot wind 

 coming from the north-east. It blows almost steadily from October to March, 

 and modifies the temperature to an extraordinary degree. Coming direct from 

 the Sahara, it is absolutely devoid of moisture, and consequently produces great 

 evaporation when it meets the moist air of the Niger Valley or the inland system 



