CRAB-HOLES, TREES, AND OTHER MOSQUITO SOURCES IN LAGOS. 265 



In Lagos C. nebulosa is, next to S. fasciata, the species most common in domestic 

 receptacles (greatly exceeding the latter in agbo pots), but in Accra C. fatigans 

 apparently always takes second place. The latter seems to be a comparatively 

 rare insect in Lagos. Apart from those bred from larvae, a few adults were cap- 

 tured in crab-holes in the GoK-course swamp in July 1914, and occasional specimens 

 have been obtained in Government Quarters in the residential area. The larval 

 sources in the period 1914 to 1918 were as follows : — Wells, 6 occasions ; boat 

 or canoe, 2 ; barrel, 1 ; total, 9. If a slight but constant degree of sahnity is 

 favourable to this species one would expect a greater prevalence. 0. irritans is 

 a very common mosquito in Lagos and probably prefers a breeding-place with 

 an appreciable amount of chlorides. It seems to have a special prochvity towards 

 crab-holes, but an equally common source is surface pools ; it also occurs in wells, 

 catch-pits, and various receptacles of domestic or pubHc utiUty ; roof -guttering, 

 canoes, and banana-tree stumps have yielded occasional samples. Curiously enough 

 0. nigricephalus, its common associate in crab-holes, does not appear to affect 

 domestic receptacles, not even wells, yet the adult insect is commonly captured 

 in houses. 



Culex decens, which freely uses crab-holes as a breeding-place, is after S. fasciata 

 the most common species in wells ; other sources were surface pools, drains, pots, 

 tubs, etc., and once each a tree-hole, agbo pot, and rain-water on a tarpauhn. 



Culex tigripes, from the predaceous habit of its larvae, is rather a welcome assistant 

 than otherwise, though its presence deranges one's estimate of other domestic 

 species. It has been found in wells, pools, pots, and once in agbo. 



Culex duttoni seems to be less common in Lagos town than at Ebute Metta on the 

 mainland. Water-pots and weUs, and once a canoe, were the only sources discovered, 

 but it has been previously found at Yaba in dirty water in tubs, barrels and ponds. 



Culex fatigans (see above). 



Culex grahami has been bred from well samples, from surface pools and borrow- 

 pits, and once from a water-barrel. 



Stegomyia luteocephala has its chief habitat in trees. The only domestic source has. 

 been the roof -gutters (from which it has also been obtained in Accra) ; a crab-hole, 

 a pool in a yard, and a telegraph-pole socket have furnished larvae on isolated 

 occasions. 



Culex guiarti was obtained on two occasions from water-pots ; it has previously 

 been found in a pond at Yaba. 



Culex insignis occurred once in a yard well ; crab-holes and surface pools are 

 usual sources. 



Culex ataeniatus was obtained once only, from a household pot. 



Culex thalassius was obtained once from a water-bucket ; away from dwelHng- 

 houses its sources are numerous, viz., pools and brackish swamps, crab-holes, canoes, 

 and once it was found in a railway girder. 



S. africana was hatched on one occasion from a sample from a household tin ; 

 it has also been obtained from surface pools, and previously from a bamboo at Yaba. 



Eretmopodites quinquevittatus was found abundantly on one occasion in a 

 potsherd in a garden in the Hospital Compound. 



