The White-Lipped Snails (Candidula unifasciata) have massively increased in numbers in the past few decades.
They are very small, around 10 mm "big", and tend to cluster in large numbers along the leaves of plants in the summer, trying to hold onto some humidity.
I took this photo during a 4 month long bike ride through Europe.
We had just arrived at a campsite in Easter Poland when these stratocumulus undulatus clouds appeared in the sky.
We just had time to find some shelter before a mighty thunderstorm broke out.