Finally got a butterfly bloom

[Blaine]

I've been playing 1.3 pretty heavily since it dropped, and this is the first time I've had a butterfly bloom. Thankfully, the home base I most often use is built over a long, flat stretch of Hallow and there are Water Candles spaced at intervals, specifically for lightning bug and butterfly blooms. I still can't resist catching as much as I can even after catching many thousands of lightning bugs and completing my butterfly collection.

Anyway, these are the results from that bloom:

I've caught one additional Tree Nymph since 1.3, which suggests that the Gold butterfly might be about twice as rare as the Tree Nymph, which is already ludicrously rare.

My entire critter collection is complete!

 

[Jeremopolis]

What's a butterfly Bloom?

 

[Blaine]

What's a butterfly Bloom?

On certain rare days, the planets align just so; the slimes gather together for a pilgrimage to the great slime graveyard; the bunnies, squirrels, and birds all sleep in until evening; and the Moon Lord slumbers more deeply than usual.

On these days, lots and lots of butterflies come out... maybe.

 

[Bethany]

At a certain moon phase, more butterflies than usual spawn in the daytime and more fireflies at night. I believe it's waxing crescent, the phase just after new moon. Not certain about that though.

Every once in a while this phase will coincide with an extra-high random spawn chance to produce clouds of bugs.

 

[Voyager]

Oh man now you are going to get me looking for these things...

 

[Foxyfluff]

Bit late but; how come this particular "event" isn't mentioned on the Wiki at all?

Also, just to compare my first and only "Butterfly Bloom" catches to yours:

0 Tree Nymph Butterfly
2 Gold Butterfly
6 Red Admiral Butterfly
1 Purple Emperor Butterfly
Others were 20+

Strangely enough I caught a Tree Nymph two In-Game days later. Effectively completing my entire collection in a little over an hour. It was accompanied by a more common Butterfly and those would be the only I'd see/catch that day.

 

[Fuzzwad]

Apparently I had one of these, there was a TON of fireflies. I didn't have my net on me, so I had to hop back in my house it was right next to it, but still. Anyway, I got my net and captured about 20-25.