Wild Wonders of Europe / Smit / Great pond snail (Lymnaea stagnalis) trying to survive in ponds in broadleaf forest during dry season, Gornje Podunavlje Special Nature Reserve, Serbia, June 2009

Nick Upton / Great pond snail (Lymnaea stagnalis) grazing aquatic vegetation in a garden pond, Wiltshire, UK, February.

Nick Upton / Great pond snail (Lymnaea stagnalis) grazing aquatic vegetation in a garden pond, Wiltshire, UK, February.

Nick Upton / Great pond snail (Lymnaea stagnalis) grazing aquatic vegetation in a garden pond, Wiltshire, UK, May.

Heather Angel / Channelled apple snail (Pomacea canaliculata) laid on Water hyacinth (Eichhornia crassipes) leaves, both invasive species, native to South America. Yangshuo, Guangxi Zhuang Autonomous Region, China.

Shane P. White / Small-leaved Fig (Ficus obliqua) trees along freshwater spring, Matevulu Blue Hole, Espiritu Santo, Vanuatu

David Fleetham / Auger shell (Terebridae) eye to eye with Skeleton shrimp (Caprellidae sp), close-up. Blurry areas in the background where freshwater is percolating up through sand and mixing with saltwater. Philippin...

Remi Masson / Great pond snail (Lymnaea stagnalis) eating aquatic plant in a river. Alps, River Rhone, France

Jan Hamrsky / Ramshorn snail (Planorbis planorbis), on piece of submerged wood, June, controlled conditions

Jan Hamrsky / Ramshorn snail (Planorbis planorbis), on stone underwater, Europe, June, controlled conditions

Jan Hamrsky / Ramshorn snail (Planorbis planorbis) on stone underwater, Europe, June, controlled conditions

Jan Hamrsky / Ramshorn snails (Planorbis planorbis), on stone underwater, Europe, June, controlled conditions