356 INSECT ARCHITECTURE. 



instant, the latent larva. At this time, if the tongue of 

 the horse touches the egg, its operculum is thrown open, 

 and a small, active worm is produced, which readily adheres 

 to the moist surface of the tongue, and is thence conveyed 

 with the food to the stomach." He adds, that " a horse 

 which has no ova deposited on him may yet have botts, by 

 performing the friendly office of licking another horse that 

 has."* The irritations produced by common flies (Antho- 

 myicE meteoriccB, MeigexJ are alleged as the incitement to 

 licking. 



The circumstance, however, of most importance to our 

 purpose, is the agitation and terror produced both by this 

 fly and by another horse breeze-fly {Gasterophilus hcemor- 

 rhoidalis, Leach), which deposits its eggs upon the lips of 

 the horse as the sheep-breeze fly ( (Estrus ovis) does on that 

 of the sheep. The first of these is described by Mr. Clark 

 as "very distressing to the animal, from the excessive 

 titillation it occasions ; for he immediately after rubs his 

 mouth against the ground, his fore-feet, or sometimes 

 against a tree, with great emotion ; till, finding this mode 

 of defence insufficient, he quits the spot in a rage, and 

 endeavours to avoid it by galloping away to a distant part 

 of the field, and if the fly still continues to follow and teaze 

 him, his last resource is in the water, where the insect is 

 never observed to pursue him. These flies appear some- 

 times to hide themselves in the grass, and as the horse 

 stoops to graze they dart upon the mouth or lips, and are 

 always observed to poise themselves during a few seconds 

 in the air, while the egg is prepared on the extended point of 

 the abdomen.'^f 



The moment the second fly just mentioned touches the 

 nose of a sheep, the animal shakes its head and strikes the 

 ground violently with its fore-feet, and at the same time 

 holding its nose to the earth, it runs away, looking about on 

 every side to see if the flies pursue. A sheep will also 

 smell the grass as it goes, lest a fly should be lying in wait, 

 and if one be detected, it runs ofl" in terror. As it will not, 

 * Linn. Trans, iii. 305. f Ibid. 



