fly
蝿 centers on the common insect: a fly. It is a specific zoological term without broad abstract extensions.
蝿 combines 虫 (insect) with a phonetic component that historically indicated the sound. The right side is a simplified form, and its exact origin is uncertain.
The insect radical 虫 on the left tells you it's a bug. The right side looks like a fly's body with wings and a curled tail, making 蝿 a fly.
For ヨウ, imagine a fly buzzing with a high-pitched 'yo' sound: yo -> ヨウ, as the fly darts around.
glowworm
stable fly (Stomoxys calcitrans)
Mediterranean fruit fly (Ceratitis capitata); medfly
fruit fly (any insect of family Tephritidae)
cucurbit leaf beetle (Aulacophora femoralis)
greenbottle fly
dung fly (any fly of family Scathophagidae)
biting midge (any insect of family Ceratopogonidae); no-see-um
flies are attracted to foul smells; ruffians flock together
phorid fly
moth fly (Psychodidae); moth midge; sand fly
flypaper
fly-net cupboard
Asian lopseed (Phryma leptostachya subsp. asiatica)
myiasis
large silvery fly
horse botfly (Gasterophilus intestinalis)