TSETSE FLIES 



491 



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, Muscidae, 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 FlG - 228. 



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- 

 FIG. 229. Head and teristic, perhaps, is the arrangement of 



mouthparts of tsetse fly; , . 



ant., antenna; ep., epi- the mouthparts and antennae (Fig. 229). 

 pharynx; hyp., hypo- Tne pro boscis consists of a bulblike base 



pharynx; palp., palpus; . *" . 



lab., labium; label., label- which is continued as a slender shaft, com- 



--ant. 



---label. 



lower U P with tw 



needle-like puncturing organs within it, one 

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

 the salivary juices. The proboscis proper is ensheathed in the 

 maxillary palpi which are so grooved as to conceal entirely the 



