BIONOMICS OF TSETSE, ETC., IN THE GOLD COAST. 207 



Bequaert mentions the case of a carnivorous spider as a natural enemy of tsetse, 

 whilst I myself found a predatory Attid spider, Plexippus paykulli, And., capturing 

 G. palpalis on the Government steamer on the Gambia.* 



Dragonflies have also been seen devouring tsetse, but by far the most important 

 insect enemies are Asilid flies and wasps of the genus Bembex. 



Four species of the former were captured by me with tsetse in their grasp. One of 

 these is an undetermined species of Asilus, while the others are indeterminate both 

 as regards genus and species. Although several species of Asilidae have been seen 

 capturing and devouring tsetse, some take to it more readily than others. I caught 

 a large number with G. tachinoides, but very few with G. submorsitans. At one place 

 on the Lora River, between Daboya and Larabanga, I fitted up a large mosquito net 

 and enclosed in it numerous tsetse and a few Asilidae. It was noted that most of 

 the tsetse were caught on the wing, only a very few being taken while resting. When 

 an Asilid captures a tsetse, it becomes so engrossed in its prey that it is possible to 

 approach it very closely and note its modus operandi. They seldom fly any great 

 distance after a capture, but alight on some small adjacent twig. Grasping the twig 

 on both sides with the tarsi of all six legs, the Asilid presses the abdomen of the tsetse 

 with all its femora, and inserts its proboscis into the thorax. Although the abdomen 

 be distended with blood, the Asilid very seldom punctures it, but presses the blood 

 into the thorax, and there abstracts it. On a very, few occasions I saw the Asilid 

 transfer the proboscis from the thorax to a point between two segments of the 

 abdomen, and suck the blood from there. 



The toll of tsetse taken by Asilidae is considerable. They follow cattle and horses 

 long distances, and I have repeatedly seen an Asilid grasp a tsetse about to alight on 

 a horse's neck. Sometimes they will hold a fly for over a quarter of an hour, 

 occasionally shifting the position of the proboscis five or six times. I have also seen 

 them relax their hold of the twig when disturbed, fly away with the tsetse and 

 return to almost the identical spot again. Of 24 tsetse put into a mosquito net with 

 six Asludae, all were dead within 24 hours, and all showed signs of having been 

 punctured. 



Bembex is the most voracious enemy of G. submorsitans. These insects seem to 

 abound more in the open country than in the shady regions inhabited by G. tachinoides. 

 Roubaud states that a species of Bembex attacked and captured G. longipalpis, but 

 was not seen in the palpalis area. On one occasion at Larabanga my pony was 

 surrounded by G. submorsitans and also small Tabanids.f Numerous Bembex were 

 hovering about and not a few tsetse were captured, although in no case did I see the 

 Bembex attempt to take the Tabanids. The Bembex does not alight, but darts quickly 

 down and either captures the tsetse on the wing or immediately it has alighted. I 

 tried an experiment with tsetse and Bembex in a mosquito net in all respects similar 

 to that with tsetse and Asllidae, with the same results. 



Thus the Asilidae are the chief insect enemies of G. tachinoides and Bembex of 

 G. submorsitans. Whether or not it would be feasible to breed and disperse these 

 insects it would be highly injudicious to state categorically. 



* Bull. Ent. Research, ii, p. 210. 

 f See section (m). 



