108 
NATURAL HI8T0BY 
mistaken wlien he advances that this CEstrus 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 CEstrus 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. 
ISIr. Bracy Clark, who has well described the habits of these insects 
in his " Observations on the Genus CEstrus," 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 sufiicient to bring forth in an 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 fi-om thence 
conveyed into the stomach." For the manner in which the larva affixes 
