Lightning Bug

One good night in the Hallow fills a stack faster than any crafted bait chain. Flatten a run of hallowed grass near wherever you sleep, come back after dusk and sweep it with a net. How many turn up gets rolled fresh every evening, so a thin night is not a broken farm, just come back tomorrow. New moon nights are the ones worth waiting for.

Firefly Statues produce these as well, but anything a statue spawns bursts into smoke the moment a net touches it. If you want bait you need wild ones. The statue is only useful as a light source or as scenery.

What it needs is hallowed grass, not hardmode itself. Spread the Hallow into a world where no altar has been broken and these will still appear at night, which makes it the one creature in the game that can turn up ahead of its own tier.

Outside the game the two names describe the same insect. Terraria splits them into a pair of critters and sorts them by biome, cyan in the Hallow and yellow everywhere else.