On a day distracted by a momentous national election, here is something wholly unrelated — the beautiful creatures called velella velella. As lovely as they are, these jellyfish, also known as “purple sailors” or “by-the-wind sailors,” can be an unwelcomed visitor. Last spring, velella velella by the thousands drifted onto Hallandale Beach, about 18 miles north of Miami. 

“This happens about every three years. We are flying our Purple flag for dangerous marine life,” city officials said on social media. Similar incidents occurred on Pacific Northwest beaches in 2015.