BLOOD-SUCKING INSECTS AND TROPICAL DISEASES. 169 



taries of Abyssinia "* the late Sir Samuel Baker speaks of herds of game 

 between the Setit and Atbara Rivers retreating before the attacks of Serut-flies. 

 The species of Hcemaiopota and Chrysops, and the smaller species of Tabanus 

 ' are remarkable for the quietness with which they alight on their victims, the 

 sharp prick of the bite being often the first intimation of the presence of the 

 fly. The larger species of Tabanus betray their approach by their loud hum. 

 Leptidse (no English names known). 



The Leptidse are a small but widely distributed family of slenderly built 

 flies of moderate size. Their inclusion among blood-sucking forms is due to 

 individuals of four different species having been observed in a small number of 

 instances to suck human blood ; but since the Leptidas normally prey upon 

 other insects the blood-sucking habit is certainly exceptional and perhaps to be 

 ascribed to individual aberration. The species in the case of which the habit 

 has been recorded are an undescribed Symplwromyia, the female of which, 

 according to Baron Osten Sacken, who observed it near Webber Lake, Cali- 

 fornia, in the month of July, bites quite painfully " and draws blood like a 

 Tabanus" ; the common European Leptis scolopacea, Linn, (of which both 

 sexes have been stated to bite) and L. strigosa, Mg. ; and Trichopalpus obscurus 

 Phil., a species with an elongated proboscis, common in the Province of 

 Valdivia, Chile, in December and January, and said to be a greedy blood-sucker. 

 The observations with regard to the two species of Leptis were made in France. 



Appearance. — Narrow-bodied flies, from 6 mm. to 13 mm. in length, with 

 long legs and with the abdomen usually tapering towards the tip. The eye 

 meet together in the males above the small antennas, but are separate in the 

 females. The proboscis is usually short and fleshy, occasionally elongated, 

 the venation of the wings resembles that of the Tabar.ida?. As a rule some 

 shade of brown or yellowish brown forms the prevailing colour, and the 

 wings are frequently blotched with brown. When at rest the wings are 

 carried flat or nearly so, diverging widely at the tips. 



Life-history. — The oviposition of the alleged blood-sucking species has not 

 been obsei'ved. According to Beling, the larva? of Leptis, which are shining 

 white or yellowish in colour, with a small brown head, and four papilla; 

 arranged in the form of a square on the anal segment, subsist chiefly upon 

 earthy and decaying vegetable matter, and are found for the most part in 

 woods, beneath the carpet of leaves or pine-needles, as well as in decaying tree- 

 stumps, etc. The same author states that the larvas of Leptis may be distin- 

 guished at the first glance from other similar larva;, such as those of II amatopot a 

 by certain characteristic markings on the upper side of the first two body seg- 

 ments, by the structure of the anal segment, and specially by their great mobili- 

 ty. The larva of Symphoromyia crassicornis, Pz., a European species, was found 

 by Beling under turf at the edge of a beech- wood. It is described as measuring 

 12 mm. in length, dirty white in colour, tapering somewhat towards both 

 extremities, with a small brown head. 



* London : Macmillan & Co., 1367, p. 210. 



on 



a - 



