M U S 
in default of eyes, which they appear to want, feera to nfe 
it to feel for and feize the aphides; when they have found 
one of them, they pierce it with the dart at their mouth, 
then draw it within the fecond ring of their body, and at 
their eafe fwallow their prey ; and thus they continue de¬ 
touring them one after another. As thefe larvae feed 
folely on aphides, lbrne naturalifts have called the flies 
which they produce mujfcee aphidivorce, or aphis-eaters. 
The larvae of other flies feed on the flelh of dead animals 
and other decayed fubftances ; the blue fielh-flies are of 
this number: every one knows how difficult it is In the 
fummer to keep meat from their attacks; they depofit 
their eggs on it, the meat is then called fty-blomi; foon 
after, maggots are hatched from them, and thefe are the 
larva; of the blue flefli-fly. Larvae of this kind, though 
With trouble and difficulty kept from the larder, may on 
the whole be coniidered as ufeful to mankind, inafmuch 
as they deftroy and carry away putrid fubitances. The 
larvae of fome of thefe flies, efpecially that of the Mufca 
Ctefar, a Ihining green fly very common in hedges and 
gardens, are not content however with the flefli of dead 
animals, but attack living ones. The harmlefs and ufeful 
animal theflieep is particularly obnoxious to their attacks, 
and not unfrequently. The flieep knows its enemy, and 
tries all in its power to avoid it, but in vain : the fly uiu- 
ally fettles on the rump, where it is leaft liable to be mo- 
lelted, and there among the wool lays its eggs; thefe, 
when hatched, quickly find their way to the Ikiri of the 
animal, which having deltroyed they penetrate into the 
flefli; and, when they happen to be depolited near the 
abdomen, frequently enter the bowels of the animal, and 
deftroy it. Sometimes the flieep is attacked in feveral 
parts at the fame time ; thus diieafed it has motions pecu¬ 
liar to itfelf, and will frequently wander from the reft, 
hide itfelf in fome hedge or ditch, and die unoblerved. 
The fkilful and attentive fhepherd feldom lofes any of his 
flock from this caufe; be quickly difeovers the malady, 
and without lofs of time applies a remedy, cuts off the 
wool, clears away the larvse, and pours train-oil into the 
wound, to which he fhould add fome oil of turpentine. 
Cheefe in a decayed ftate, and bacon not thoroughly 
cured, are the favourite food of the larvae of another fpe- 
cies of fly, much fmaller than the preceding; the dealers 
in thefe articles give to thefe larvae the name of hoppers. 
If attentively obferved, they may be feen to form them- 
felves into a kind of ring, and with great elafticity throw 
themfelves to the height of five or fix inches. Swammer¬ 
dam was the firft that noticed this manoeuvre, and has 
deferibed it with that accuracy for which he is diftin- 
guiflied. It is the M. putris. Muddy and flunking- wa¬ 
ters, fuch as drain from dunghills and neceflaries, are the 
favourite abodes of another fet, differing conliderably 
in their make from the above, having their bodies fur- 
nilhed with a long tail; hence they have been called by 
Reaumur vers u. queue do rat, or rat-tail maggots; fuch 
are frequently obferved in the country creeping about 
neceflaries. A very remarkable circutnftance attends 
.thefe ; they have no fpiracula, or breathing-holes, in the 
body, as the other larvae have, but the tail is tubular, and 
they breathe through an orifice at the extremity of it; 
when in the water, they are faid to be capable of extend¬ 
ing this tail five inches if necefi'ary, and are frequently ob¬ 
ferved carrying it to the furface of the water to draw in 
air : we may obferve, that the liquor in which thefe larvae 
are found is generally (hallow. 
A few lpecies of flies live in their larva ftate after the 
manner of ichneumons ; in the bodies of living cater¬ 
pillars we have frequently-obferved them produced from 
the larvae of the Phaltena potatoria, or drinker-moth, as 
well as the Phaltena falicis, iatin-moth whether they lay 
their eggs on the outfide, or whether they pierce the fkin 
of the caterpillar, we have not yet had an opportunity of 
obferving. Moll kind of fungi, or mulhrooms, as they 
decay, are full of the maggots of .various flies. The larvae 
of fome flies live in, the heads of the compound flowers ; 
Vol. XVI. No. nop. 
C A. 25i 
others on the parenchymatous orflefhy part of the leaves 
of trees and plants, betwixt the two lkins; fome in the 
ftallcs of thirties, where they produce extraordinary 
tubercles; in fliort, the habitations of the feveral Ipe- 
cies are fo numerous, that it would be taking up too 
much time to mention all of them ; we have enumerated 
thofe of the moft confequence, and by them we fee that 
the maggots of flies are by no means an inactive fet of 
beings, but of great confequence in the ceconomy of 
nature. 
Fondas thefe infefts are in their larva ftate of filth and 
putridity, in their perfedl ftate they are more delicate in 
the choice of their food, fupporting themfelves generally 
by the nedtar which they fuck from flowers ; there are, 
however, a few inftances to the contrary. Though, in 
general, a very harmlefs genus, we are acquainted with 
two fpecies that are of a fanguinary nature, and which 
feed on the juices of other flies, which they previoufly 
kill : the Mufca ftercoraria, or dung-fly, which we gene¬ 
rally obferve on cow-dung, is one of this lort; there is 
another fpecies fomewhat fimilar to it, but lefs hairy, 
found occafionally in the (hop-windows in London, and 
doubtlefs elfewhere ; firft obierved by Mr. Benjamin 
White, fen. of Fleet-ftreet, bookfeller, in his (hop-win¬ 
dows, feeding on the Mufca domeftica, or common houfe- 
fly. One would think that the trunk of this infedt was 
ill adapted for an inllrument of death; but certain it is 
that it makes ufe of it to pierce the body, as well as to 
fuck the juices, of the fly. We have many times been an 
eye-witnels to it: on placing this fly, which we call neca* 
trix, under a wine-glafs with the Mufca domeftica, we 
have feen it prefently feize, kill, and fuck its blood. The 
chief difference that we difeern in the probofeis of this 
and other flies is, that,it is ftronger and apparently much 
differ. 
Flies, after they have gone through their changes, are 
not long before they copulate: this adt is performed in 
a very Angular manner ; for here the part of the male is 
open, and receives the female inllrument, which enters 
the body of the male, to have the eggs impregnated. In 
noticing this manoeuvre, fo contrary to what we obferve 
in all other animals, one is ready to think onefelf mif- 
taken as to the fadt, and that the female muft receive 
the male part; indeed, authors of no (mail reputation, 
deceived by its appearance, have confidered and figured it 
fo; but the obfervations of later authors have clearly 
proved the contrary; indeed this required no extraordi¬ 
nary dilcernment, for, befides that the bodies of fuch flies 
as have the penis-like inllrument, which ealily protrudes 
on preffing the abdomen, are larger than the others, on 
placing it before a moderate magnifying-glafs, one may 
dillindtly difeern the eggs, than which no greater proof 
can be adduced of its being a female. Thefe parts are 
admirably represented in a highly-magnified ftate, by Mr. 
Keller, before-mentioned, who has molt clearly and fatif- 
fadlorily decided this matter. The infertion of the female 
inllrument is only to be feed in fuch flies as are actually 
in copulation, and in which ftate, the female, having ab- 
folute dominion over the male, flies with him, where lire 
lifts; not in thofe temporary attempts at copulation, 
which flies are perpetually exhibiting. 
The generality of flies are oviparous ; a few are vivipa¬ 
rous, that is, bring forth larvae initead of eggs ; fuch pro¬ 
duce a final 1 number of young, compared with the ovipa¬ 
rous ones. 
Next to Phalasnse, or moths, the genus Mufca is by far 
tfle mod numerous in point of fpecies, and of thefe there 
are many that have feveral broods in a year; the common 
houfe-fly is one of this fort. When we coniider that in 
one fealbn a Angle female houfe-fly is capable of pro¬ 
ducing twenty millions eighty thoufand three hundred 
and twenty, (Keller’s calculation,) we (hail not wonder 
at their fwarming lb much in autumn. This fpecies 
breeds chiefly about (tables and in neceflary-houfes ; and 
near Inch they will always be found moll numerous. 
3 T Varioul 
