118 



falling victims. But although I have spent many hours watching in 

 suitable places at the edge of the forest or in open sunny spots in tha 

 forest (localities frequented by Asilidae) where Glossina abounded, an 

 Asilid has only once been seen preying upon Glossina." 



Carpenter's statements as to dragonflies on Lake Victoria are sup- 

 ported by Fiske (54), who writes : " A dragonfly of a rather small and 

 undetermined species occurs commonly, but irregularly distributed, 

 throughout the islands and riparian belt. There are other species, but 

 this one is conspicuous for its numbers and for a well-marked habit of 

 following moving animals and man and feeding off the flies which are 

 attracted to them. Large numbers in exceptional cases perhaps as 

 many as 40 or 50 of these dragonflies may follow a man along the 

 open shore, and they have been observed to capture tsetse many times. 

 " The species varies greatly in local density from one island or 

 district to another. It was observed most abundantly along the 

 western shore of Bukone Island in September 1914. A fairly complete 

 survey of the island was made, and the infestation indicated (male 

 density 8-6 ; female ratio 23-4 per cent.) was considerably lighter 

 than conditions, apart from the very exceptional number of dragonflies, 

 would have led one to expect. It seemed quite probable that the 

 destructor was responsible for a considerably less heavy infestation 

 than would otherwise have occurred. 



" There is this difference between spider and dragonfly that 

 sheltering vegetation is of little or no protective value against spiders, 

 but of much protective value against dragonflies. They will not 

 follow a moving animal into cover, and the flies are not likely to be 

 captured unless they hunt in the open " (cf. also p. 117 above). 



Information on the subject of dragonflies as enemies of G. morsitans 

 in Nyasaland is contained in a paper by Dr. Lamborn (83), which 

 appeared in December 1915. 



"A species of dragonfly (Orthetrum chrysostigma, Burrn.), the male 

 dull blue in colour, the female greenish blue/' writes Lamborn, " has 

 now been found to prey on morsitans. In February, in the Lingadzi 

 district, I saw one of these dragonflies, which had been following and 

 hovering round the party of six boys with me, suddenly swoop down 

 and take a tsetse from the back of one of the boys who was stooping 

 at a pool to drink, its movements being extremely rapid. It settled 

 on the grass near by and commenced to devour its prey. Later on 

 I saw a dragonfly of the same species take a morsitans which had 

 rested on a blade of grass, though again I was unable to see whether 

 the capture was effected on the wing or not ; and on the following 

 day I saw another capture a tsetse off a boy. A fact of importance 

 in all three cases was that each dragonfly accompanied our party for 

 some little distance, obviously expecting to find its prey in our vicinity. 

 " I have further studied these dragonflies in relation to morsitans 

 in the Monkey Bay district. They have been observed repeatedly 

 to flit round passers-by as if in search of prey, settling near by if 

 unsuccessful. When a number of people are walking in Indian file, it 

 is quite common for the insects to make a search round each, often 

 following on a short distance behind, and I have without any difficulty 

 caught a number of specimens with their prey, in most cases tsetses, 

 taken in the neighbourhood of natives accompanying me." An 

 annotation by Dr. G. A. K. Marshall states that " Dr. Lamborn has 

 sent notes of 21 cases in which he saw these dragonflies take tsetses 

 on 23rd and 24th April and 3rd to 12th May 1915." 



