5 1 2 DIPTERA CHAP. 



while in the third instar there is a greater diversity in the 

 condition of the breathing apertures. 



The various forms of Muscidae show considerable distinctions 

 in the details of their natural history, and these in certain species 

 vary according to the locality. This subject has been chiefly 

 studied by Portschinsky, a Russian naturalist, and a very interest- 

 ing summary of his results has been given by Osten Sacken, 1 

 to which the student interested in the subject will do well 

 to refer. 



A few years ago a great deal of damage was caused in the 

 Netherlands by Lucilia sericata, a Green-bottle-fly, extremely 

 similar to our common L. caesar, which deposited its eggs in 

 great quantities on sheep amongst their wool. This epidemic 

 was attributed to the importation of sheep from England ; but, 

 according to Karsch, there is reason to suppose that the fly was 

 really introduced from Southern Europe or Asia Minor. 2 



The larvae, of species of the genus Lucilia sometimes attack 

 man and animals in South America, but fortunately not in this 

 country. The larva of Lucilia (Compsomyia) macellaria is called 

 the screw- worm, and is the best known of the forms that infest 

 man, the larvae living in the nasal fossae and frontal sinuses, 

 and causing great suffering. The fly is common in North 

 America, but is said never to attack man farther north than 

 in Kansas. A little fly (Stomoxys calcitrans), very like the 

 common house-fly though rather more distinctly spotted with 

 grey and black, and with a fine, hard, exserted proboscis, 

 frequently enters our houses and inflicts a bite or prick on us. 

 It is commonly mistaken for an ill-natured house-fly that has 

 taken to biting. It is frequently a source of irritation to cattle. 

 A closely allied fly, Haematohia serrata, is very injurious to cattle 

 in North America, but the same species causes no serious annoy- 

 ance in England. We may mention that the various attacks of 

 Dipterous larvae on man have received the general name 

 " myiasis." 



The Tse-tse fly (Glossina-morsitans), another ally of Stomoxys, 

 is not very dissimilar in size and shape to the blow -fly. 3 



1 Berlin, ent. Zeitsclir. xxxi. 1887, p. 17. 



2 Biol. Centrum, vii. 1887, p. 521. 



3 For an account of the habits of this fly, see Kirk, 7. Linn. Soc. viii. 1865, pp. 

 149-156 ; and for a bibliographic list, Wulp, Tijdschr. Ent. xxvii. 1884, p. xci. and 

 pp. 143-140. 



