Sulphur butterfly salt lick. These male sulphur butterflies are congregating on a damp river bank in order to extract salt from the mineral-rich mud. This process is called puddling. The insect inserts its proboscis into the mud and draws up the salt in the water. The salt is then passed on to the female in the male's sperm during the mating process. Photographed in the Amazon rainforest, Ecuador.