THE r.REEZE-FLIES. 637 



The generic name Gasterophilus is formed from two Greek 

 words, and signifies ' belly-loving.' It has been given to the 

 insect in consequence of the habits of the larvae. It is rather 

 a pretty insect, and has some resemblance to an Andrena, 

 The thorax is black, partly covered witli warm chestnnt down, 

 and the abdomen is alternately banded with ruddy chestnut 

 and black. The wings are slightly clouded with brown. 



Theee are several other insects belonging to this family, 

 each of which selects some particular animal for its home. 



There is, for example, the WunnLE Bkeeze-fly, or Gad-fly 

 {^(Estrus hovis), the economy of which is very remarkable, the 

 creatiu-e seeming to produce much the same effect upon the ox 

 that the gall-flies do upon plants. Instead of being taken into 

 thp stomach of the animal, as is the case with the last-mentioned 

 species, this species never penetrates further than the skin. 



Into the skin the larva burrows as soon as hatched, and it is 

 remarkable that the female insect takes as much care to place 

 the egg on the back where the tongue of the ox cannot reach 

 it, as the Bot-fly to place the egg where the tongue of the 

 horse has easy access to it. Beneath, or rather in, the thick- 

 ness of the skin, the larva makes its residence, its head being 

 downwards and its wide tail upwards, so as to receive air into 

 the two spiracles which are there placed. The habitation of 

 the Wurble, as the grub is called, is made evident by a small 

 swelling, in the upper part of which is an opening through 

 which the tail end of the larva can be seen. 



When it is full-fed, the larva retrogrades out of its habita- 

 tion and falls to the earth. No sooner is it fairly on the 

 ground than it begins to burrow,, and then undergoes its trans- 

 formations underground, exactly as has been stated of the 

 Bot-fly. The colour of this species is brownish, the base of the 

 abdomen is covered with grey down, and the rest is ruddy 

 chestnut. ^ 



Then there is the Sheep-flt {(Estrus ovis), a smaller, greyer, 

 and more slender species. The female of this insect selects 

 the nostril of the sheep as the place whereon she is about to 

 deposit her eggs. The sheep are very m\ich afraid of this 

 insect, and do all in their power to rid themselves of theii 



