144 INJURIOUS AND USEFUL INSECTS 



of animals. They are fertilised by the female immediately 

 before laying, the sperms having been previously received 

 from the male, and stored up in a special receptacle within 

 the abdomen. 



The blow-fly exhibits the following marks of a Dipterous 

 insect: — -(i) There is one pair of transparent wings, and a 

 pair of halteres. (2) The mouth-parts include piercing organs 

 (here quite insignificant), and a suctorial labium (here un- 

 usually large, and capable of protrusion and retraction). 



The following points are characteristic of the sub-order 

 Athericera : — (i) There are short antennae, with three enlarged 

 basal joints and a bristle. (2) The piercing mouth-parts are 

 reduced to two slender and pointed styles, one in front of 

 the other ; there is a pair of unjointed maxillary palps, and 

 a large suctorial labium ending in two broad lobes. (3) The 

 pupa is enclosed in a puparium, formed by the hardened 

 larval skin, which bursts transversely to allow of the escape 

 of the fly. 



The antennae sunk in a cavity on the face, the plumose 

 bristle springing from the base of the third joint of the 

 antenna, the well-developed proboscis, and the halteres 

 covered by a winglet, indicate that the blow-fly belongs to 

 the Muscinae, Muscids of the highest grade. — 



29. THE BOT-FLY OF THE HORSE (Gastrophilus equi) 



Horses at pasture are often plagued with this insect. The 

 egg-laying fly is seldom noticed; it is over half-an-inch (13- 

 17 mm.) long, with brownish-black hairs, speckled wings and 

 yellow legs. In the male fly the abdomen is nearly globular, 

 but in the female it is drawn out into a long, curved, several- 

 jointed extremity, which is employed as an egg-laying tube. 

 The fly is rather sluggish, and easily caught; it flies with a 

 humming or buzzing sound. In autumn (August to October) 

 such flies are now and then seen about horses ; they settle 

 for a moment on the horse or the clothes of the horseman, 

 and then fly away. After a few visits from the fly, the horse 

 pays little attention to them, only showing by the twitching of 

 his skin-muscles that they tickle him a little. Little does 



