How does a tarantula get bigger? It doesn't have skin that stretches like us, and it doesn't have scales that shed like a snake. Instead, it molts, which basically means they have to grow a new exoskeleton (hard exterior) each time they outgrow their current one. When this happens, the tarantula produces a substance that helps separate itself from the old exoskeleton. Then, it grows a new one and shimmies out of its old one! This process can take up to 15 hours, and the tarantula spends the whole time on its back! Hey, it might be weird, but it works for them.