蓼食う虫も好き好き
(Tade kuu mushi mo sukizuki;
“Even the bug who eats knotweed likes it”)

Definition:

Yet again, “different people have different tastes.” A person can like a thing that you don’t (or vice-versa), and that’s okay. Even spicy plants have insects that like to eat them.

Breakdown:

We begin with the noun 蓼 (tade), any of a number of more-or-less edible plants in the Persicaria genus of the knotweed family. Any following particle is elided, but we may imagine an (を) marking this noun as the direct object of the verb 食う (kuu), “to eat,” here in prenominal form, attached to and modifying the noun 虫 (mushi), “insect.” This is followed by the emphatic particle も (mo), which often serves as “also,” but here is probably something closer to “even.” And finally we get the noun 好き好き (sukizuki), a set phrase meaning something like “a matter of taste” or “personal preference.”

Notes:

Although the kanji 蓼 is not part of the contemporary standard set, and in contrast to some other sayings with the writing adjusted for ease of reading, this one always seems to be written with 蓼 instead of substituting in any sort of kana. On the other hand, 好き好き may occasionally be replaced with equivalent phrase 好き不好き (suki busuki), which emphasizes that “personal taste” includes both likes and dislikes.

Knotweed, sometimes called “smartweed,” is not usually cultivated, although it it is one of the standard wild edible plants known as 山菜 (sansai). Making it edible takes a bit of work; it generally requires soaking, boiling, or pickling, and even then has a sharp taste. It’s also used as a spice, and in a number of folk medicines. In most of the world it is a tough and aggressive invasive species.

A number of sayings play with the same basic idea as this one: the insect that eats tade knows no bitterness (蓼の虫苦きを知らず, tade no mushi nigaki wo shirazu); it won’t abandon its home to move to a mallow plant (蓼の虫葵に移らず tade no mushi aoi ni utsurazu); it will die on the tade after spending its whole life there (蓼の虫は蓼で死ぬ, tade no mushi wa tade de shinu).

It appears that the 蓼の虫 is in fact a specific species: Monolepta dichroa, a leaf beetle that doesn’t seem to have a common name in English but is known in Japanese as ホタルハムシ (hotaruha mushi, traditional kanji 蛍金花虫), presumably so named because of a superficial resemblance to actual fireflies.

Example sentence:

「ゴマアイス食べたい！」　「えーっ、チョコが良い！」　「意地悪言わないでよ！蓼食う虫も好き好きじゃん」　「お前虫じゃねぇやろ」

(“Goma aisu tabetai!” “Eh, choko ga ii!” “Ijiwaru iwanaide yo! Tade kuu mushi mo sukizuki jan.” “Omae mushi ja nee yaro.”)

[“I want sesame ice cream!” “Ugh, chocolate is better!” “Don’t be mean; even knotweed has a bug that likes it.” “You’re not a bug, though!”]

I hate chocolate! Leave it for the humans.