259 



NOTES OX BLOOD-SUCKING FLIES IN GRENADA. 



By Angus Macdonald, M.D., D.P.H.. 



Medical Officer in Charge, Inter nadomd Health Connnission, Grenada. 



(Plates III & l\.} 



Grenada is the southernmost of the string oflslands composing the Lesser Antilles, 

 if we except Trinidad and Tobago, some ninety odd miles further south, which lie 

 close to the South American mainland of Venezuela. Geologically the Island is 

 volcanic ; basalts, lavas, cinder beds, gravel beds, agglomerates, various earths or 

 clays forming the soil and subsoil of valleys, slopes, ridges, cones and craters, from sea- 

 level to some 3,000 feet of elevation. 



The Island is clothed in vegetation ; rather scanty bush for varying distances by 

 the sea margin, natural forest on the higher ridges, and a carpet of dense cacao and 

 fruit-tree growth on the main part of the land. The mountain ridges are central, 

 tlie cultivation zone surrounding them and extendir.g to the sea, except where the 

 margin of scrub stretches for varying widths along the littoral. 



The ground rises from the sea rapidly, and the population — with the exception of 

 those living in the few small coast towns, about one-sixth of the whole — live by 

 agriculture in the cultivation zone at elevations roughly between 300 and 1,500 feet. 

 There are of course some dwellers by the sea and some small holders higher in the 

 mountains ; and the Island may be considered to be inhabited all over, though to 

 the ordinary traveller the forest heights are not too smoothly accessible. 



Meterologically, it may be remarked in brief that the temperature is equable, and 

 a mean of 80° may be accepted for the whole year with little variation and trifling 

 range. The rainfall, though more concentrated in the June and November periods, 

 is well distributed throughout the year, and while there is no disconcerting humidity, 

 and the Trades blow ever fresh from the East, the combined effect of rainfall and 

 vegetation is to maintain moist subarboreal conditions. 



Owing to the nature of the cultivation (arboreal in the main) and tiie climate, the 

 natural life of the cultivation zone differs little fiom that of the forest zone ; elevation 

 and the scattered presence of man causing the chief difference. The significance of 

 this fact may. be observed in these notes ; and another example of it is seen in the 

 habits of the monkeys {Cercopilheciis ihoiki), wliich live in the forest ranges, but 

 regularly come down to quite low elevations to regale themselves on the growing 

 cacao-pods, bananas, etc. Among mosquitos. Liinaltis dnrhami seems as happy 

 breeding in a broken bottle under cacao a few hundred feet above soa-level as in a 

 palm-leaf petiole in the mountain forest at 2.()(U) feet. 



For the identification of tiu' insects here consiilered 1 am indebted to the Wellcome 

 Bureau of Scientific Research, whose Director-in-Chief, Dr. Andrew Balfour. GM.(!., 

 has given me much other scieiitific assistance during my stay in the A\ est Indie>. 

 Mr. Malcolm MacGrejior, Entomolojiist to the Burean. n^- well a> making manv of the 



