Researchers are predicting that the number of non-native species will rise by about 36 percent worldwide by 2050. Non-native, or alien species, are plants or animals that humans have moved around the world to places where they are not naturally found. Sometimes the introduction of an alien species to an area is accidental. Sometimes, it is done on purpose. Research shows the movement of plants and animals rose across the planet over the last century as human trade and travel opened up new worldwide pathways. A new study predicts such movements are likely to continue, with the largest increases expected to be big insects, birds and small creatures such as mollusks and crustaceans. Researchers are calling for more rules and better observation methods to help reduce the spread of alien species.