虫 was originally a pictograph of a coiled snake — head at top, body curled around itself. Ancient Chinese taxonomy lumped all small long-bodied creatures (snakes, worms, insects, centipedes, lizards) under a single category, and 虫 named the whole class. Traditional script preserved the distinction: 虫 alone meant "snake / small creature," while 蟲 (three 虫 stacked together) specifically meant "insect / a swarm of small creatures." Japan and Mainland China both standardized on the simpler 虫 for both meanings; Korea retains the traditional 蟲 for "insect" in formal vocabulary.

As a radical, 虫 anchors a vast taxonomy of crawling, flying, and slithering creatures: 蟻 (ant), 蚊 (mosquito), 蛇 (snake), 蝶 (butterfly), 蜂 (bee), 蛙 (frog), 蜘蛛 (spider). Almost any animal name with a small body and lots of legs — or no legs — uses the 虫 radical.

Korean reading "chung." 害蟲 (haechung, pest insect — economic damage to crops), 益蟲 (ikchung, beneficial insect like ladybugs and bees), 寄生蟲 (gisaengchung, parasite — also the original Korean title of the Oscar-winning film), 昆蟲 (gonchung, insect — the formal scientific term), 毒蟲 (dokchung, venomous bug).

Mandarin chóng, 2nd tone. 虫子 (chóngzi, bug / worm — generic colloquial term), 昆虫 (kūnchóng, insect — scientific), 害虫 (hàichóng, pest), 寄生虫 (jìshēngchóng, parasite). Modern Chinese usage closely parallels Korean.

Japanese on-reading チュウ (chū) — 昆虫 (konchū, insect), 害虫 (gaichū, pest), 寄生虫 (kiseichū, parasite). The kun-reading むし (mushi) generates wonderfully evocative compounds: 虫 (mushi, bug), 虫歯 (mushiba, "bug-tooth" = cavity, since East Asian folk etymology blamed tooth decay on a tiny worm eating the tooth), 泣き虫 (nakimushi, "crying-bug" = a crybaby), 弱虫 (yowamushi, "weakling-bug" = coward). Most poetic of all: 腹の虫が治まらない (hara no mushi ga osamaranai, "the bug in my belly won't settle down") — a Japanese idiom for "I'm so angry I can't calm down," picturing rage as a literal worm in the gut. Also 腹の虫が鳴く (hara no mushi ga naku, "the belly-bug is crying") = "my stomach is growling."

Memory aid: a coiled creature seen from above. Originally any small wriggling thing — eventually all the bugs, worms, and slithering creatures of the world.