DuneCraft® Spider Balls™ science kit. Drop one of the Spider Balls in water and find out how they got their name: A multitude of multicolored balls will burst forth from the green sac and grow up to 100 times their original size within hours! You can control the size range of the "spiders" by adjusting the amount of water you add. Try rolling, throwing, bouncing and squishing the balls once they are hydrated-they slip, slide, and explode! 1 kit per package.