For the purpose of this map, I opted to go for dots rather than fully colored regions, as some areas may use multiple forms and I don't know the exact boundaries of where forms are used.
It's worth noting that the forms used by some regions may apply to both butterflies and moths. Some words that refer to both could also refer to just moths in other areas (not mapped here). This is the case of kakabe/kakkabe, for example.
It's also important to note that this map is strongly dialect-oriented. In truth, the forms chō, chōchō and chōcho would be the most widely used words today. Areas on the main islands that have no markers are most likely to use these forms, but I wasn't able to confirm this due to a lack of data.
- There's a fairly sharp contrast between Japanese dialects, which favour forms based on chō, and the Ryukyuan languages [blue area in the south], which favour forms based on *paperu.
- Dialectal forms based on chō + X (chōma, chonma, etc.), where X represents another morpheme, are a lot more common in the North and even in Kanto than I expected.
- In a lot of the terms related to butterflies, the sound *pira (hira, hera, hiru, etc.) appears to be a recurrent theme. Compare Ryukyuan *paperu, Old Japanese *pipiru 'silkworm moth', Iwate tebirako (< te + no + hira + ko), Saitama chōchōbakko (< chōchō + hera + ko), Middle Japanese kawahirako (< kawa + hira + ko), Nagano amabira 'small butterfly', etc.
For anyone curious: Korean uses 나비 nabi, which is clearly not related. However, according to the Wiktionary, it originates from the root *nAp meaning "flat, wide". This is similar to the Japanese term ひら【平】 hira 'broad, flat'.