XP can be gained in many ways. Some of these ways are getting rid of Ant Lions and Stinky Bugs, helping Ladybugs, completing missions on the right hand side of the screen, buying decorations, and finishing tasks with your bugs. Finishing tasks with the piles and flowers all have different amount of XP earned when they are completed depending on the size and time it takes to finish them. Over time, this achievement will unlock; just keep playing!
Note: This achievement is extremely glitchy! It can unlock at a range of different levels. People have reported this unlocking as early as level 17 and others have had to reach past level 26 before it unlocked.