Water currents enter and exit from caves. Aquatic fauna do the same and Nepa can fly easily or enter in crevices if it senses water. That said, the species show

Water currents enter and exit from caves. Aquatic fauna do the same and Nepa can fly easily or enter in crevices if it senses water. That said, the species shown are strange for Europe. I wouldn't discard that there are some misplaced photos (or the authors toke some literary licenses).