Critters Common

Purple Glowbug紫色の光虫

This flying bug always appears in swarms which appear as dancing lights. Its purple glow is biome-specific.
In-game description

What is Purple Glowbug? Features and uses

Purple Glowbug is a common item in Core Keeper (Critters).

Purple Glowbug key points (from the game data)

Sells to merchants for 1 Ancient Coin.

Calculated and summarized by this site from the game data (1.3.0.6).

Purple Glowbug notes

It gives off a faint purple light.
Swing a Bug Net at the Purple Glowbug to catch it; it then goes into your inventory like any other item.

These notes cover behavior that the game files do not show directly. They are based on facts from the Core Keeper Wiki (Fandom) page "Purple Glowbug" (CC BY-SA 3.0), rewritten in this site's own words.

How to get Purple Glowbug

Placed naturally when the world is generated (Breaker's Reach)From the game's world generation settings (Conf/Spawn/Initial).