(Image Credit: U.S. National Weather Service)

A mysterious cloud that appeared on weather radar over southern Illinois and Central Missouri last week turned out to be a swarm of monarch butterflies.

Meteorologists from the National Weather Service analyzed the shape-shifting cloud that was moving toward Mexico to figure out what exactly it could be.

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"We think these targets are Monarch butterflies.," the National Weather Service said in a Facebook post. "A Monarch in flight would look oblate to the radar, and flapping wings would account for the changing shape!"

With the mystery solved, the fine folks at the NWS wished the butterflies "good luck and a safe journey" on their trip south for the autumn and winter.