TSETSE FLIES 



491 



Fig. 228. 

 position. 



Tsetse fly in resting 

 X 4. (After Austen.) 



General Form. — The tsetse flies (Fig. 228) are elongate, dark 

 brown or yellowish brown flies, some species no larger than an 

 ordinary housefly, others larger than 

 blowflies. They are usually in- 

 cluded as an aberrant group of the 

 housefly family, Muscidse, but from 

 other members of the family they 

 differ in a number of striking ways, 

 especially in the manner of repro- 

 duction, and in form of the larva. 

 They constitute the genus Glossina 

 which contains 15 species and has 

 no very close allies; some species 

 are of very wide distribution, while 

 others are local or very rare. Tsetses 

 can most easily be distinguished 

 from other flies by their position 

 when at rest (Fig. 228) ; their wings 

 are folded flat, one directly over the other, straight down the 

 back, like the blades of a pair of scissors, while the proboscis 

 projects horizontally in front of the head. 

 Beyond these characteristics there is noth- 

 ing strikingly distinctive about a tsetse fly, 

 and it is therefore difficult for anyone who 

 is not thoroughly familiar with it to identify 

 it on the wing. The darting manner of 

 flight and buzzing sound are said to be 

 quite diagnostic when one is once familiar 

 with them. When the flies are caught and 

 examined, however, there are a number of 

 good identification marks. Most charac- 

 teristic, perhaps, is the arrangement of 

 the mouthparts and antennae (Fig. 229). 

 The proboscis consists of a bulblike base 

 which is continued as a slender shaft, com- 

 posed of a grooved lower lip with two 

 needle-hke puncturing organs within it, one 

 of which, the hypopharynx, contains a deHcate tube for carrying 

 the salivary juices. The proboscis proper is ensheathed in the 

 maxillary palpi which are so grooved as to conceal entirely the 



-r label. 



Fig. 229. Head and 

 mouthparts of tsetse fly; 

 ant., antenna; ep., epi- 

 pharynx; hyp., hypo- 

 pharynx; palp., palpus; 

 lab., labium; label., label- 

 lum; sp., spiracle. (After 

 Alcock.) 



