THE GAD-FLY, WURBLES, OR WORMALS 485 



recollect to have seen, in the summer months, a whole 

 herd of cattle start off across a field, at full gallop, as 

 if they were racing, their movements indescribably 

 awkward their tails being poked out strait and stiff 

 behind them, and their necks stretched forward to 

 their utmost length. All this consternation has been 

 known from the earliest times to be caused by the 

 appearance of the gad-fly. 



If Mr Clarke's views be correct, when the egg of 

 the ox-fly is hatched, the grub (Plate x, fig. 17) im- 

 mediately burrows under the skin, where it feeds upon 

 the fatty matter, and remains until it has reached 

 maturity. As the grub continues to grow, the bumps, 

 or wurbles, increase in dimensions, in proportion to 

 the size of the grub (Plate x, fig. d). It is not until the 

 middle of May that these bumps can be seen full 

 grown ; but, owing to particular circumstances, they 

 do not attain an equal size. The largest of these are 

 sixteen or seventeen lines in diameter by the base, and 

 about one inch high, but they are scarcely perceptible 

 before the beginning, or during the course of the 

 winter. 



Young cattle are most commonly attacked by these 

 insects, and the most healthy are fixed upon for the 

 deposition of their eggs ; a wonderful proof of the 

 instinct of these flies. Cattle-dealers and farmers 

 have remarked this fact, and the latter always find the 

 hides the best that these flies prefer. The number of 

 bumps, or wurbles, which are found upon a beast, is 

 equal to the number of eggs which have been de- 

 posited in its flesh ; or, to speak more correctly, the 

 number of eggs which have become matured under 

 the skin, as those which have been fertile. Some- 

 times there will be found a single wurble on a cow, 

 while in others upwards of thirty have been counted. 



