108 NATURAL HISTORY 



mistaken when lie advances that this (Estrus is the parent 

 of that wonderful star- tailed maggot which he mentions 

 afterwards ; for more modern entomologists have discovered 



sometimes by that of bots, are found beneath the skin of cattle : these 

 are the larvae of the true (Estrus bovis, the perfect fly of which was 

 probably unknown to the great Swedish naturalist. The maggots of 

 the other, known, in common with those of some other species, by the 

 name of bots, are found with the larvae of those other bot-flies in the 

 stomachs of horses. The one whose habits are described by White, 

 may be called the spotted- winged bot-fly. 



Mr. Bracy Clark, who has well described the habits of these insects 

 in his " Observations on the Genus (Estrus," published in the third volume 

 of the " Linnean Society's Transactions," and subsequently in an " Essay 

 on the Bots of Horses," says : " The female bot-fly approaching a horse 

 on the wing, holds her body nearly upright in the air, and her tail, 

 which is lengthened for the' purpose, curved inwards and upwards : in 

 this way she approaches the part where she designs to deposit the egg ; 

 and suspending herself for a few seconds before it, suddenly darts upon 

 it, and leaves the egg adhering to the hair : she hardly appears to settle, 

 but merely touches the hair with the egg held out on the projected point 

 of the abdomen. The egg is made to adhere by means of a glutinous 

 liquor secreted with it. She then leaves the horse at a small distance, 

 and prepares a second egg, and, poising herself before the part, deposits 

 it in the same way. The liquor dries, and the egg becomes firmly glued 

 to the hair : this is repeated by various flies, till four or five hundred 

 eggs are sometimes placed on one horse. 



" The inside of the knee is the part on which these flies are most fond 

 of depositing their eggs, and next to this on the side and back part of 

 the shoulder, and less frequently on the extreme ends of the hairs of the 

 mane. But it is a fact worthy of attention, that the fly does not place 

 them promiscuously about the body, but constantly on those parts which 

 are most liable to be licked with the tongue ; and the ova therefore are 

 always scrupulously placed within its reach. Whether this be an act of 

 reason or of instinct, it is certainly a very remarkable one." Mr. Bracy 

 Clark suspects, with Dr. Darwin, it cannot be the latter, as that ought 

 to direct the performance of any act in one way only. 



The eggs thus deposited are not, in Mr. Bracy Clark's opinion, re- 

 moved from the hairs by the moisture of the horse's tongue, aided by its 

 roughness, in the act of licking, and thus conveyed to the stomach : but 

 remain, he conceives, attached to the hairs for four or five days until 

 they have become "ripe, after which time the slightest application of 

 warmth and moisture is sufficient to bring forth in an instant the latent 

 larva. At this time, if the tongue of the horse touches the egg, its 

 operculuni is thrown open, and a small active worm is produced, which 

 readily adheres to the moist surface of the tongue, and is from thence 

 conveyed into the stomach." For the manner in which the larva affixes 



