VI DIPTERA 251 



The PsYCHODiDAE include Phlebotomus a small black " Sand-fly " or 

 midge which may be recognized by its sharp almost flea-like darts from 

 side to side, and by the characteristic fashion in which it holds up its 

 wing when biting. It is the transmitting agent of " Sand-fly Fever " or 

 " Three-day Fever " or " Pappataci Fever " (p. 80). 



The TiPULiDAE include Tipula, the Daddy-long-legs, the underground 

 larva of which (" Leather- jacket ") does much damage to crops. 



The SiMULiiDAE include the very blood-thirsty midges or sand-flies 

 of the genus Simulium, with large clear wings, which occur occasionally 

 in swarms in Britain and in some warmer climates form a great pest. 



The Tabanidae include the many species of Gad-flies, Horse-flies and 

 Clegs. The common noiseless light-footed " Cleg " belongs to the genus 

 Haematopota. The genus Chrysops, in which the eyes are often golden- 

 green and the wings partially dark in colour (Widow Fly or Viuda of 

 Spanish T^erica), is incriminated as the transmitter of Filaria loa 

 (p. 206). 



The Syrphidae include many of the most abundant kinds of flies. 

 Some of them present a remarkable mimicry of Bees and Wasps, and 

 these have possibly given rise to the ancient legend of Bees coming forth 

 from decaying matter such as carcases. 



The MusciDAE include a number of the most abundant types of fly, 

 some of them of practical importance in connexion with the spreading 

 of disease. They are characterized by their short three-jointed antennae 

 with a jointed, sometimes feathery, bristle projecting from the terminal 

 segment. 



The common large House-fly (Musca domestica, identified by the four 

 dark lines which run along the dorsal surface of the grey thorax), world- 

 wide in its distribution, does a certain amount of useful work as a 

 scavenger, but any good that it does in this way is far overbalanced by 

 the harm that it does in spreading diseases of the alimentary canal such 

 as Tjrphoid, and where large numbers of non-immune human beings are 

 crowded together under conditions favourable to the microbes of such 

 diseases its control becomes of the greatest practical importance. 



The eggs, to the number of about 800 from a single female, are 

 deposited in rotting material or preferably in fresh faeces of horse or 

 man. After about twelve hours ^ the larva, a slender white grub or 

 maggot rounded at its hinder and pointed at its front end, hatches out. 

 The larva grows rapidly to a length of about 12 mm., and after about 

 5-8 days crawls into a dry spot and metamorphoses into the pupa, and 



1 These time periods are greatly shortened by warmth and lengthened by 

 cold. 



