41G 
CE‘ S T R U S. 
botts.'’ When tlie animal is kept from food, the boits are 
alfo, and are then, without doubt, the moft troubiefbme; 
whence it was very naturally fuppofed, that poverty or 
bad food was the parent of them. 
4- CEftrus veterinus, the veterinary gad-fly : wings im¬ 
maculate ; body ferruginous; white hairs on the Tides of 
the thorax and at the bafe of the abdomen. 
This fpecies feems to have been well defcribed by Lin¬ 
naeus, who called it naj'ulis, from an idea of its entering 
the noftrils of the horfe to depoiit the eggs, which it could 
not well do without deflroying the wings, and is there¬ 
fore probably as much a fable as the “ mire per anum 
intrans” of the CE. haemorrhoidalis. The chryfalides of 
this fly have been uniformly found under the dung of 
liorfes. They produced the fly reprefented at fig. 8. If 
the larva inhabited the fauces of the horfe, it would pro¬ 
duce fuch troublefome fymptoms as could not eafily ef- 
cape the notice of thole wbofe bufinefs it is to attend to 
the difeafes of cattle. Such a difeafe has, however, never 
been defcribed by any w'rifer on this fcience; nor, after 
an extenfive opportunity, both in the dead and living fub- 
je£t, of obferving them, have I ever (fays Mr. Clark) feen 
a bott in the fauces. Perhaps the botts oftheftomach hav¬ 
ing crawled to the fauces in fearch of food might have 
given rife to this idea; or they may even have acciden¬ 
tally bred there, for there is little doubt thefe animals 
can live in any part whatever of the alimentary canal. 
“ I am induced to fufpeft they inhabit the ftomach, as 
well as the two former fpecies; but of this we muff: at 
, prefent remain in uncertainty, as well as of the manner 
in which this fpecies depolits its eggs. J have given it 
the name of veterinus, becaufe beads of burden are par¬ 
ticularly fubjeft to it, in preference to the erroneous one 
of nnfalis." 
5. CEftrus ovis, the fheep gad-fly: w ings pellucid, 
punctured at the bafe; abdomen variegated with black 
..and white. 
The larva of this fpecies is reprefented at fig. 9. It is 
nearly as large as that of the CE. equi,of a delicate white 
colour, flat on the under fide, and convex on the upper; 
■ having no fpines at the divifions of the fegments, though 
they are provided with tentacula at the final 1 end. The 
other end is truncated with a prominent ring or margin, 
which ferves the fame purpofe in an inferior degree as the 
lips of the CE. equi and haemorrhoidalis, by occafionally 
clofing over, and cleaning, the horny plate. When this 
margin opens, after clofing over the plate, it occafions 
frequently a flight fnap from the fudden admiiTion of the 
/air. When young, thefe larvae are perfe&ly white and 
tranfparent, except the two horny plates, which are black. 
As they increafe in fize, the upper fide becomes marked 
with two tranfverfe brown lines on each fegment, and 
feme fpots are feen on the fides. They move with con- 
ilderable quicknefs, holding with the tentacula as a fixed 
point, and drawing up the body towards them. On the 
■ under fide of the larva is placed abroad line of dots, 
which, on examination with glafles, appear to be rough 
points, ferving perhaps the double purpofe of aflifting 
their paflage over the fuiooth and lubricated furfaces of 
thefe membranes, and of exciting alfo a degree of inflam¬ 
mation in them where they reft, lo as to caule .a fecretion 
of lymph or pus for their food. 
Mr. Clark fays, “ I have moftly found thefe animals in 
the horns and frontal finufes of the fheep, though I have 
remarked that the membranes lining thefe cavities w'ere 
hardly at all inflamed, while thofe of the maxillary finufes 
verchighly fo. From this I am led to expeft theyinhabit 
the maxillary finufes, and crawl, on the death of the ani¬ 
mal, into thefe fituationsin the horns and frontal finufes. 
The breeds of thefe, like the CE. bovis, do not appear 
confined to any particular feafon ; for quite young and 
full-grown larva; may be found in the finufes at the fame 
time. When full-grown, they fall through the noftrils, 
and change to the pupa ftate, lying on the earth, or ad¬ 
hering by the fide to a blade of grafs. The fly burfts the 
fiiell of the pupa in about two months. See fig. 10. 
The manner in which this fpecies depofits its ova has, 
I believe, not been defcribed ; nor is it eafy to fee, though 
clofe to the animal at the time, exa&ly in what way it 
is accomplifhed, owing to the obfeure colour and rapid 
motion of the fly, and the extreme agitation of the fheep ; 
but the motions of the fheep afterwards, and the mode 
of defence it takes to avoid it, can leave but little doubt 
that the egg is depofited on the inner margin of the nof- 
tril. The moment the fly touches this part of the fheep, 
they fliake their heads, and ftrike the ground violently 
with their fore-feet; at the fame time, holding their 
nofes clofe to the earth, they run away, looking about 
them, on every fide, to fee if the fly purfues : they alfo 
fmell to the grafs as they go, left one fhould be lying in 
waitforthem. If they obferve one, they gallop back, or 
take fome other direction. As they cannot, like horfes, 
take refuge in the water, they have recourfe to a rut, or 
dry dufty road, or gravel-pits, w'here they crowd together 
during the heat of the day, with their nofes held clofe to 
the ground, which renders it difficult for the fly conve¬ 
niently to get at the noftril. Obfervations on thefe flies 
are belt made in warm w'eather, and during the heat of 
the day, when, by driving the fheep from their retreats to 
the grafs, the attack of the fly, and the emotions of the 
fheep, are eafily oblerved.” 
The obfervations of Mr. Clark extend no farther than 
to thefe five fpecies; and he concludes with fome remarks 
as to the mode by which they might be deftroyed, though 
he feems to doubt whether their prefence is very injurious 
to the cattle or not; he feems to think that the irritation 
they occftfion often protefts the cattle from more ferious 
ailments. But he fays, “ If, after mature enquiry, the 
exiftence of the CEftri fhould be proved in a greater de¬ 
gree injurious than any fervice they can afford, their 
numbers might be confiderably reduced, and a total ex¬ 
tirpation of fome of the fpecies, w’ould, I am difpofed to 
believe, be not altogether impracticable. The injury de¬ 
rived from their depredations is principally felt by the 
tanners, whofe hides are often fo perforated by thefe ani¬ 
mals as to be confiderably damaged thereby ; and the lofs 
of a horfe or a fheep may fometimes perhaps be occalioned 
by the exiftence of the other fpecies. 
“ If it were defirable to lefien their numbers, the fol¬ 
lowing, I apprehend, would be the moft fuccefsful means : 
The larva of the CE. bovis, which breeds in the backs of 
the horned cattle, is fo confpicuous, that it is more eafily 
deftroyed than the others: the injeftion of any corrofive 
liquor into the finus w'ould kill it; or, by puncturing the 
larvae with a hot needle, introduced through the apertures 
in the fkin, or even by Ample preflure, they may be de¬ 
ftroyed, afterw'ards extracting them, or leaving them to 
flough aw'ay, which I have frequently obferved they da 
when crufhed by a blow from the horn of the beaft, or by 
any other accident, without material injury to the animal. 
A man employed for this purpofe might, in half a day, in 
this manner, deftroy every bott on'a large common. 
In regard to the CE. equi and hsemorrhoidalis, thofe 
who have horfes which have been much out to grafs the 
preceding year, in countries w'here thefe flies are preva¬ 
lent, might confiderably dimiriifh their numbers, by 
examining the horfes occafionally for the botts during 
the months of May and June, w'hen they will be found 
hanging to the extremity of the reftum, where they 
remain for fome time before they fall to the ground. 
The deftruftion of a fingle one at this feafon of the 
year, is not only the death of an individual and its 
effedfs, but the almoft certain deftruCtion of a whole fa¬ 
mily ; at the fiyne time it is alfo highly ufeful, in prevent¬ 
ing the irritation which the fpines of the bott oceafion to 
the anus. If the horfe is ufed on the road w'hile the bott is 
adhering to this part, the irritation becomes diftrefling, 
and cattles him to move very awkwardly and lluggifidy, as 
though 
