The story
From being a mine that has an appearance reminiscent of a butterfly.
Etymology from Wiktionary, CC BY-SA 4.0.
Today it means: A type of winged air-dispersed and air-dropped anti-personnel landmine, typically without metal parts, so undetectable by usual metal detectors for landmines; looking like a child's toy. Full definition →
From being a mine that has an appearance reminiscent of a butterfly.
Etymology from Wiktionary, CC BY-SA 4.0.