The rare painted lady butterfly has been spotted in the U.K. and Ireland, a once-in-a-decade phenomenon. The painted lady or Vanessa cardui emerge every 10 years when weather conditions and food sources are ideal for their survival.

Over 11 million painted lady butterflies were spotted in 2009, the last time they emerged.

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An employee at the Royal Botanic Garden in Edinburgh, Scotland told the BBC that he's seeing thousands of painted ladies at the moment, as opposed to the usual 10-15 in the gardens.

Painted lady butterflies can travel up to 100 miles in a day and the numbers will likely increase in the coming months – although that increase depends on temperature, wind conditions, and more.

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[h/t BBC]