"Con chuồn chuồn"
Why do name of some bugs seems to have repeating words?
firefly - con đom đóm dragonfly - con chuồn chuồn grasshopper - con cào cào / con châu chấu
The same thing happens across many tonal languages. It is likely to do with the sounds associate with the creature or for alliteration to make the name sound prettier. Another example is a butterfly which can be either bướm or bươm bướm.
That's interesting since I don't know either. I grew up asking the same question. One theory is that (I guess) these words are of phonogram (based on the sound that these creatures make when they fly/move around).
I asked my Vietnamese friends neither and they said a similar thing. For 'firefly' specifically, they said the word 'sounds like how it looks' - if that makes sense.
(classifier con) chuồn chuồn
1) a dragonfly
Chuồn chuồn bay thấp thì mưa, bay cao thì nắng, bay vừa thì râm.
It will be sunny if dragonflies fly low, rainy if high, neither if so so.
chuồn chuồn kim (“damselfly”)
From Wiktionary: https://en.wiktionary.org/wiki/chu%E1%BB%93n_chu%E1%BB%93n