SIMULIIDAE OF AFRICA 9 



the spinous comb that precedes them provide useful characters, since they differ 

 between taxa. In the mature larva of some forms the cervical sclerites are linked 

 by continuous (although sometimes weaker) sclerotization to the upper ends of the 

 postocciput (Text-fig. 20), but in the majority of forms they form small discretely 

 isolated platelets in the neck membrane (Text-figs. 14 & 21). 



The shape of several morphological structures of the larva (such as the head 

 sclerites, hypostomium and postgenal cleft) alters during larval development, and 

 the number of several other structures increases (such as the number of cephalic fan 

 rays, antennal segments, cuticular setae, and hooks in the posterior circlet) : it must 

 be emphasized, therefore, that the larval characters cited in the keys and diagnoses 

 throughout the text are those of mature or almost fully developed larvae. 



GEOGRAPHICAL DISTRIBUTION OF SIMULIIDAE IN AFRICA 



AND ITS ISLANDS 



The family Simuliidae is found throughout continental Africa wherever suitable 

 watercourses exist for the pre-imaginal stages. It is only absent completely from 

 areas of utter desert (most of the Sahara and Kalahari deserts). The family is known 

 from all but three of the African states : there are no records as yet from the arid 

 desert states of Libya, Spanish Sahara, and Mauritania. In the Arabian peninsula 

 Simuliidae occur in South Yemen Republic (near the Yemen border), but are 

 unknown from the Hadhramaut. 



In the islands around Africa the distribution of Simuliidae is as follows : present 

 in the Canary Islands, Fernando Po, St. Helena, Madagascar, Comoro Islands, La 

 Reunion, Mauritius, Rodriguez and the Seychelles ; absent from Ascension Island, 

 Tristan da Cunha, Gough Island and Aldabra ; unknown from the Cape Verde 

 Islands, Principe, Sao Thome\ Annobon and Socotra (but none of these islands 

 surveyed for Simuliidae). 



Simuliidae in North (Palaearctic) Africa reach a southern limit at about 30 °N. 

 (in Morocco), and in Ethiopian Africa reach a northern limit at about 15 °N., except 

 down the valley of the Nile where the Ethiopian fauna penetrates northwards to 

 about 25 °N. ; but between these latitudes, which approximately delimit the desert, 

 Simuliidae are recorded from two central Saharan massifs (Tibesti and Tassili des 

 Ajjer). 



The altitudinal range of Simuliid breeding in Africa is from sea-level to 14,700 ft. 

 and altitude in general is not a significant factor in determining distribution, which 

 appears to be governed primarily by geological considerations — for the geological 

 history has determined the geographical position and hydrological characteristics of 

 the river and stream systems that are suitable for development of the immature 

 stages. Thus, in the detailed picture of distribution, Simuliidae are found to be 

 present most evidently in areas where the Precambrian basement rocks of Ethiopian 

 Africa form the land surface and give rise to rocky-bedded rivers and streams ; in 

 other areas where marine incursions have overlaid the Precambrian basement with 

 sedimentary deposits of much later periods (usually Cretaceous and Tertiary) the 

 watercourses tend to be sandy or muddy and Simuliidae absent or less universally 



