CRAB-HOLES, TREES, AND OTHER MOSQUITO SOURCES IN LAGOS. 253 



species of Ochlerotatus were often associated. C. decens, C. nehulosa and 

 V. annulata were all hatched from one sample. In another instance 0. irritans, 

 0. nigricephaluSj U. annulata and C. nehulosa were in association. 



(2) Adult Mosquitos in Crah-holes. 



A few collections were made of imagines found in crab-holes. The dates of these 

 fall between the months of May and October, 1914, and representatives of 17 species 

 were determined, viz. : — 



Ochlerotatus irritans 



„ nigricephalus 

 „ caliginosus 



Culex fatigans 



„ consimilis 

 Uranotacnia annulata 



„ punctothoracis 

 Culex decens 

 ,, insignis 

 ,, thalassius 

 „ rima 

 ,, salishuriensis 



,, hilineata var. fraseri 

 Culiciomyia nehulosa 

 Mansonioides africanus 

 Anopheles costalis 

 Stegomyia fasciata 



The order of arrangement in the above list is not necessarily that of frequency 

 of occurrence, and the number of individuals caught was insufficient for a true 

 estimate of relative abundance of each species. A comparison of the two foregoing 

 lists shows (1) that of the 14 species bred from larvae 2 have not been captured as 

 adults in the crab-holes, viz., S. luteocephala and M. inconspicuosus, of which the 

 larvae were obtained only once each ; (2) that pf the 17 species caught in the winged 

 state 5 are not represented in the list of larvae, viz. , 0. punctothoracis, 0. caliginosus, 

 C. fatigans, C. consimilis, and M. africanus. If these 5 could be regarded as occupying 

 at the time of capture their place of hatching, the number of species definitely 

 associated with crab-holes would be 19. The peculiar habit however of the larva of 

 M. africanus in relation to the roots of the water lettuce (Pistia stratiotes) suggests 

 its being only a temporary visitor after hatching in a pool or swamp near by (the 

 locality was the Golf-course swamp and the month July in the rainy season). 



With regard to the other 4 species, the larvae of 0. punctothoracis and of 

 0. caliginosus have not been found in any of the collections from any source in 

 Lagos during the period covered by these notes, but both have previously been 

 obtained from borrow-pits on the mainland within the municipal area. 



The adults of both species have been caught occasionally in the houses of Europeans, 

 and those of 0. caliginosus were accompanied in crab-holes at a considerable distance 

 from other possible breeding places by those of C. decens, which has already been 

 shown to be one of the commonest species hatched from this type of nidus. 

 C. consimilis has been bred from larvae taken from wells in Ebute Metta (on the 

 mainland within the municipal area), and the adult appears not very infrequently 

 in collections from the houses of European officials in Lagos itself. In crab-holes 

 the mosquito was accompanied by adults of C. decens and S. fasciata, while all 3 

 species were captured simultaneously in adjoining European quarters. C. fatigans 

 has been hatched from larvae found in wells and barrels, and occasionally in a 

 boat or canoe. It is not a common mosquito in Lagos, but has been caught in 

 European houses. It is probable that all 4 species occasionally make use of crab- 

 holes as breeding-places. 

 (713) E 



