Spiny softshell turtles are mainly carnivores that eat fish, crustaceans, and insects, but they can occasionally eat leafy greens. Greens such as mustard, turnip, and collard greens, as well as kale, offer spiny softshells plenty of nutrition and should be offered as food on occasion. Lettuce on the other hand is usually very low in nutrition. Iceberg lettuce, the most popular lettuce, has little more nutrition than tap water. It’s really nothing more than green, leafy water, so it should not be fed to your pets.