136 INSECTS AND MAN 



eighty-eight days, according to the temperature ; in nature 

 the warmth of the sun probably shortens the period. 



Two MOKE DISEASES TRANSMITTED BY FLIES 



Working in Malta, many years ago, Pym described an 

 obscure fever whose origin remained a mystery till 1908, 

 when Doer in Hertzegovina showed that it was caused by a 

 so-called sand fly, Phlebotomus papatasi (fig. 36). Doer's 

 experiments have recently been confirmed by Birt and 

 others, and the disease is now known as Phlebotomus fever. 

 In the family Psychodidce there are hairy, moth-like flies, 

 called owl midges, and blood-sucking insects, known as 

 sand flies. Phlebotomus papatasi is a very minute, pale 

 yellowish fly, rendered conspicuous by its very long legs, 

 which enable it to hop like a flea. It is somewhat widely 

 distributed, being found in Malta, South Europe, North 

 Africa, America, and North India. The female, which, by 

 the way, is the blood-sucker, for the males do not bite, lays 

 about forty of her translucent eggs in caves and cracks in 

 walls ; after a few hours the eggs lose their translucency and 

 become shining, dark brown, and marked with longitudinal, 

 slightly raised, black wavy lines. In about nine days the 

 larvae emerge ; they resemble small greyish- white caterpil- 

 lars, with dark heads and two stiff tail bristles, which become 

 four when the larva is full grown. The pupa is a curious 

 object with a triangularly shaped head, which, viewed end 

 on, resembles a ram's head in miniature, the antennal sheaths 

 appearing like horns ; in colour it is yellowish buff. 



Various experiments have been carried out in London 

 and Malta, with a view to obtaining data as to the disease- 

 carrying power of these flies. They show that a person 

 suffering from Phlebotomus fever carries the virus in his 

 blood during, at least, the first day of fever, and that a 

 sand fly, having partaken of a meal of infected blood, 

 remains infective for from seven to ten days. 



All the insects considered in this chapter, with one excep- 



