This is a relatively clear-cut poem, but there are of course many translation challenges beyond just the literal meaning of the words, including: the overall effect/intent, the sound, and the format of a tanka being 5/7/5/7/7 for a total syllable count of 31 (sort of, as syllables are not quite the same in the two languages). Below is the Japanese followed by several translations, all by people far more knowledgeable than I, and who have all translated many more pieces than just me obsessing over this one specific poem for ages. The version I have here would not have been possible without their work for reference.

ありと見て手にはとられず見ればまた
Ari to mite / Te ni wa torarezu / Mireba mata
行方も知らず消えし蜻蛉
Yukusue mo shirazu / Kieshi kagerou

Murasaki Shikibu, Genji Monogatari

There–you can see them,
But not catch them in your hand,
And when you look again
They have vanished, who knows where,
These ephemerids of dusk.

Edwin A. Cranston, Waka Anthology: Grasses of Remembrance

I see the drake fly, take it up in my hand.
Ah, here it is, I say–and it is gone

Edward Seidensticker, 1976 English translation of the Tale of Genji

There it is, just there, yet ever beyond my reach, till I look once more,
and it is gone, the mayfly, never to be seen again.

Royall Tyler, 2001 English translation of the Tale of Genji

In modern Japanese, the kanji 蜉蝣 with the gloss “tonbo” is translated as “dragonfly” or (less frequently) “damselfly”. 蜉蝣 with the gloss “kagerou”, alongside the feel of the poem in specifically conveying an ephemeral quality, makes a connection to the ephemerid mayfly more explicit.

The last two words (kieshi kagerou/vanishing ephemerid) have alliteration in Japanese. To keep the alliteration, I could go with “disappearing dayfly” or, less accurately,  “disappearing damselfly/dragonfly” where the latter options actually happen to hit the same syllable count. And “damselfly” has a fun contrast with Mister Bug… who knows, I might change my mind and edit this again in the future.

Ultimately I went with dayfly to match the intent of the poem, losing a syllable in English. I could’ve made up for it by making it “the disappearing dayfly”, but I didn’t like the addition of the particle, so just pause an extra breath before you read the last line and we’re good. 🙂