Пошу прощения, с "москитом" я погорячился, там все оказалось проще:
mosquito
1580s, from Sp. mosquito "little gnat," dim. of mosca "fly," from L. musca "fly," from PIE root *mu- (cf. Skt. maksa-, Gk. myia, O.E. mycg, Mod.Eng. midge, O.C.S. mucha), perhaps imitative of the sound of humming insects. Colloquial form skeeter is attested from 1839.
Да, «латинское» слово «мошка» - впечатляет.
gnat
O.E. gnætt "gnat, midge, mosquito," earlier gneat, used of various small, flying insects, from P.Gmc. *gnattaz (cf. Low Ger. gnatte, Ger. Gnitze); perhaps lit. "biting insect" and related to gnaw.
The gnatte is a litil fflye, and hatte culex..he soukeþ blood and haþ in his mouþ a pipe, as hit were a pricke..And is a-countid a-mong volatiles..and greueþ slepinge men wiþ noyse & wiþ bytinge and wakeþ hem of here reste.
Равно, как и слово «гнет», «гнуть», «гной».

Gnat (зnæt. Sax) a slinging fly. 1675
Gnat, s. a small winged biting insect; χγιψ. S gnaet from Gnaw
Gnaw, v.a. to bite, grind with the teeth, eat by degrees, corrode (ага, corrode – «латинское» слово. Вот только, как быть с русским жуком – короедом?); G. gnata; Isl. naga; Swed. gnaga; D. gnawe; B. knaogen, T. gnagen; S. gnagan. W. cnoi 1826

Гнести – др. русск. = жать, давить, теснить (Дьяченко)
Там же – гнесь – нечистота, грязь
Там же – гной – болячка, навоз, кал.