For example, Florida apple snails (Pomacea paludosa) are an amphibious fresh water mollusk.[86] They have a single gill and lung, and live on stalks of sawgrass in water depths no more than 20 inches (51 cm). They are the primary food of the endangered snail kite (Rostrhamus sociabilis) and limpkin (Aramus guarauna) as well as the raccoon, otter, and young alligator. Apple snails lay their eggs on sawgrass stalks about 6 inches (15 cm) above the water line, and they are intolerant of being submerged for long periods of time. When the eggs hatch, young snails must enter the water quickly or face death. When water levels are too low or rise too quickly while snail eggs are developing, apple snails do not flourish, affecting the many reptiles, mammals, and birds that feed on them.[87] With regard to the ecology of trophic dynamics, or food chains, the 174 species of invertebrates play a vital role in the Everglades.[88] Crayfish, insects, scorpions, and other invertebrates also support a web of animals.