Insect is middle plus a line at the bottom, which for the purposes of this mnemonic, we'll call a "stinger."
So you can say,
a cavity (literally, 'bug tooth,' because parents would tell their kids, 'If you get a cavity, bugs will crawl in the hole and nest and lay eggs.')
insect, (a more scientific term than 'むし')
parasite (literally, 'close living insect')