CE S T R U S, 41 r, 
dre'd are loft for one that arrives at the perfect Hate of a fly. 
The eggs,in thefirft place, when ripe, often hatch of them¬ 
felves, and the larva, without a nidus, crawls about till it 
dies ; others are wafbed off by the water, or are hatched 
by the fun and moifture, thus applied together. When 
in the mouth of the animal, they have the dreadful ordeal 
of the teeth and maftication to pafs through. On their 
arrival at the ftomach, they may pafs, mixed with the mafs 
of the food, into the inteftines; and, when full-grown, 
on dropping from the anus to the ground, a dirty road or 
water may receive them. If on the commons, they are 
in danger of being crufhed to death, or of being picked 
up by the birds who fo conftantly for food attend the 
footfteps of the cattle. Such are the contingencies by 
which Nature has wifely prevented the too-great increale 
of their numbers, and the total dellrudtion of the animals 
they feed on.” 
Thefe larvae attach themfelves to every part of the fto¬ 
mach, but are generally molt nuifierous about the pylorus, 
and are fometimes, though much lefs frequently, found 
in the inteftines. Their numbers in the ftomach are very 
various : often not more than half a dozen ; at other times 
more than a hundred ; and, if fome accounts might be 
relied on, even a much greater number than this. They 
hang moft commonly in clufters, being fixed by the final! 
end to the inner membrane of the ftomach, which they 
adhere to by means of two fmall hooks or tentacula. 
When they are removed from the ftomach, they will at¬ 
tach themfelves to any loofe membrane, and even to the 
Ikin of the hand. The body of the larva is compofed of 
eleven fegments, all of which, except the two laft, are 
furrounded with a double row of horny briftles directed 
towards the truncated end, ami are of a reddifti colour, 
except the points, which are black. Thefe larvae evi¬ 
dently receive their food at the fmall end, by a longitu¬ 
dinal aperture, which is fituated between two hooks or 
tentacula. Their food is probably the chyle, which, being 
nearly pure aliment, may go wholly to the compofition of 
their bodies without any excrementitious refid ue, though, 
on diffeStion, the inteftine is found to contain a yellow or 
greenilh matter, which is derived from the colour of the 
food, and Ihows that the chyle, as they receive it, is not 
perfectly pure. They attain their full growth about the 
latter end of May, and are coming from the horfe from 
this time to the latter end of June, or fometimes later. 
On dropping to the ground they find out fome conve¬ 
nient retreat, and change to the chryfalis ; and, in about 
fix or feven weeks, the fly appears. 
M. Latreille, in his Nat. Hilt, of Infedls, obferves, “that 
the gacj-fiies which attack animals are always females; and 
that males have never been found among them. The 
lame circumftance has been remarked with regard to the 
gnat; no male of which has been known to bite.” This 
(if really a fadt) is a new difcovery in natural hiftory. 
The moft fuccefsful method of obtaining the flies from 
the chryfalis, is by taking the larvae, when frefli dropped 
from the horfe, and immediately enclofing them feparately 
in balls of frelh horfe-dung, which mult be kept in a warm 
fituation, and fprinkled every fecond or third day with 
water; the animals will thus be preferved in a proper de¬ 
gree of warmth and moifture, and the flies will make their 
appearance in the ufual time. The complete infedl is 
fliowri on the Entomology Plate I. fig. 14, 15. the larva 
on Plate II. fig-. 19. the pupa at fig. 20 of the fame plate; 
and a duller of botts, taken from the ftomach of a horfe, 
on the Farriery Plate X. fig. 3, 3. vol. vii. 
3. CEftrus hsemorrhoidalis, the fmaller horfe gad-fly s 
wings immaculate, brownifli ; abdomen black, the bafe 
white,,the tip red. The larva of this fpecies needs not 
to be particularly defcrjbed, as it refembles, in almoft 
every refpedl, that of the CE. equi. Its habits are the fame, 
being feen in the ftomach of the horfe, occupying the 
fame fituation as thofe of the CE. equi, from which they 
can only be diftinguiflied by their fmaller iize and greater 
wjiitenefs. When it is ripe, and has palled through the 
inteftines, its fkin becomes of a greenifh-red hue. It ge¬ 
nerally aflumes the chryfalis ftate in about two days after 
leaving the redlum, and is then of a deep-red colour. 
After remaining in the chryfalis ftate about two months, 
the fly appears, as at fig. 7. 
This fpecies may ftiil retain the name of hcemorrhoidulis, 
without any impropriety ; not from the fuppofed hiftory 
of its entering the anus, but from the termination of the 
abdomen being red t Linnaeus having generally chofen to 
diftinguifli the infedls fo marked by that name ; alio from 
their refembling the haemorrhoids, or piles, while hanging 
to the extremity of the redlum. It fee-ms hitherto to have 
been generally believed among naturalifts, that the fe¬ 
male fly enters the anus of the horfe in a very extraordi¬ 
nary manner, to depofit its eggs. Reaumur (tom. iv.) 
relates this circumftance on the authority of Dr. Gafpuri. 
From the account of its getting- beneath the tail, we Ihould 
fufpedl the fly he law was the Hippobofca equina, which 
frequently does this. Its getting- within the redlum ap¬ 
pears to have been additional. That a fly might depofit 
its eggs on the verge of the anus is not impoffibie, though 
we know no inftance of it. But the fly would be crufhed 
in attempting to pafs the fphindter of a horle’s redlum ; 
and, having no means of holding while depofiting its 
eggs, it would be quickly evacuated with the dung. The 
whole of the ova, to the amount of two or three hundred, 
mull be depofited in one horfe, as it is impoflible, if the 
fly furvived, that it could undergo this punifhment a fe¬ 
cond time, for the heat and moifture of the redtum would 
at lead deftroy its wings. Thefe objedlions are mentioned, 
not as merely relating- to this fpecies, but that it may not 
be credited of any of them, that they really enter the body 
of the animal to obtain for their young a fituation there. 
Mr. Clark has particularly defcribed the mode in which 
this fly depolits its ova; which (lays he) having had re¬ 
peated opportunities of feeing, I can fpeak of with cer¬ 
tainty. The part chofen by the infedt for this purpofe is 
the lips of the horfe, which is very diltrefling to the ani¬ 
mal from the exceffive titillation it occafions; for he im¬ 
mediately after rubs his mouth againft: the ground, his 
fore-legs, orfometimes againft a tree; or, if two are Hand¬ 
ing together, they often rub themfelves againft: each other. 
At the fight of this fly, the horfe appears much agitated, 
and moves his head backwards and forwards in the air, to 
baulk its touch, and to prevent its darting on the lips; 
but the fly, watching for a favourable opportunity, con¬ 
tinues to repeat the operation from time to time ; till at 
length, finding this mode of defence infufiicient, the en¬ 
raged animal endeavours to avoid it by galloping away 
to a diftant part of the field. If it Hill continues to fol¬ 
low and teafe him, his laft refource is in the water, whe^re 
the CEftrus never is obferved to follow him. At other 
times, this CEftrus gets between the fore-legs of the horfe 
whilft he is grazing, and thus makes its attack on the 
lower lip ; the titillation occafions the horfe to ftamp vio¬ 
lently with his fore-foot againft the ground, and often 
Itrike with his foot, as though aiming a blow at the fly. 
They alfo fometimes hide themfelves in the grafs; and, as 
the horfe Hoops to graze, they dart on the mouth or lips; 
and are always obferved to poife themfelves during a few 
feconds in the air, whiie the egg is preparing on the point 
of the abdomen. 
The larva of the CE. hasmorrhoidalis, as well as the 
former fpecies, appears to have been termed among the 
Romans eoQ'us, which fee ms to have been a general ex- 
preftion for any kind of foft imperfedt animal, and to 
have been very analogous, and as extenfively applied, as 
the word grub is at prefent in the Englilh language. Our 
anceftors imagined that poverty, or improper food, en¬ 
gendered thefe animals, or that they were the offspring of 
putrefaction. In Shakefpeare’s Henry the Fourth, Part I. 
the oilier at Rocheiler fays : “ Peafe and beans are as dank 
here as a dog, and that is the next way to give poor jades 
the botts;”. and one of the misfortunes of the miierabl-e 
nag of Petrucliio is, that “ he is 1 b begnawn with the 
botts.” 
