Joan Croome (Member 58,963) was on a field trip with her fourth-grade students in Aurora, Oregon, US when, as she put it, ‘these jellyfish clouds joined us.’

Their sky was filled with Altocumulus floccus virga: mid-level clouds with bumpy tops and ragged bases from which streaks of falling ice crystals were trailing. The wispy tendrils, known as virga, are when ice crystals or raindrops falling from a cloud dissipate before reaching the ground. No need for alarm among the fourth-graders, in other words, when a swarm of sky jellyfish drift into view.