SIMULIIDAE OF AFRICA 57 



without neck (a few exceptions) and weakly woven, anterior margin often produced into a median 

 dorsal process. Larva : Head and cephalic fans normal. Hypostomium with usual nine apical 

 teeth, teeth usually sharply pointed and median and corner teeth prominent ; 3-7 setae in each 

 hypostomial row, rows lying more or less parallel to lateral margin of hypostomium. Head- 

 spots positive, usually boldly marked. Postgenal cleft typically small and subquadrate and 

 much shorter than postgenal bridge, sometimes represented by only a slight notch or completely 

 absent so that whole floor of head is sclerotized, in a few forms large rounded or mitre-shaped and 

 longer than postgenal bridge. Mandible normal, second comb-tooth smaller than first or third, 

 usually two mandibular serrations (some Holarctic forms with one or two supernumerary ser- 

 rations). Antenna long and slender, normally four segments but sometimes with secondary 

 annulations. Thoracic and abdominal cuticle usually entirely bare, occasionally with covering 

 of minute pale hairs or with minute spinous setae posterodorsally on abdomen. Abdominal 

 shape normal, broadest in profile at sixth or seventh segment. Ventral papillae present, usually 

 large and subconical but sometimes small and blunt. Accessory sclerites normally absent. 

 Rectal scales present (possibly exceptions). Rectal gills with or without secondary lobules. 

 Posterior circlet with 60-115 (usually 65-80) rows of 9-16 (usually 10-14) hooks. 



Bionomy. Eggs laid broadcast or clustered and adhered to substrate. Larval 

 and pupal stages non-phoretic ; attached to varied substrates, but often small 

 stones and dead leaves, usually in small slowly flowing watercourses but sometimes 

 in dashing broken cascades, some forms occasionally in habitats with little or no 

 detectable flow. Female ornithophilic. 



Distribution. Widespread throughout North America, Eurasia and Africa, but 

 occurring also in Central America and Australia, Madagascar and New Guinea. 

 Occurring also in the isolated islands of Azores, St. Helena, Seychelles, Reunion, 

 Mauritius, Rodriguez, Bonin Islands, Mariana Islands, and Caroline Islands, where 

 (except for Dexomyia in St. Helena) it is the only subgenus present. Palaearctic 

 distribution includes Iceland, Japan, North Africa and Egypt, Madeira and Canary 

 Islands. Present in southern Arabia. Recently found in Norfolk Island. 



Discussion. Eusimulium is the largest and most widely distributed subgenus of 

 Simulium and the only one that can be considered almost cosmopolitan, since it is 

 the only one that has successfully colonized the remote oceanic islands. The sub- 

 genus has an essentially Arctogaean distribution, as it is apparently absent from 

 South America (although found in the northern Neotropical areas of Mexico and 

 Guatemala) and in Australia is represented by only a single species : it is best 

 developed in the Holarctic Regions, where almost forty per cent of the species of 

 Simulium are assignable to subgenus Eusimulium. There is a much smaller 

 Eusimulium fauna in the Ethiopian and Malagasy Regions, where only some twelve 

 per cent of the species belong in the subgenus. 



The place that Eusimulium occupies as a main component of the Simulium fauna 

 in the temperate Holarctic is taken in the tropics by large endemic subgenera that 

 appear to be related to Eusimulium in many of their characters, but which are best 

 ranked as separate subgenera : these are Pomeroyellum in the Ethiopian Region, 

 Gomphostilbia Enderlein in South-East Asia, Morops Enderlein in New Guinea, and 

 Psilopelmia Enderlein in the Neotropical Region. The differences and resemblances 

 between Eusimulium and Pomeroyellum are considered in detail in the discussion 



