Depending on the type spider, a spider can use a powerful bite to fend off predators. Some even have venom that delivers a powerful toxin. Spiders, while having no vertebrae, do have an exoskeleton. This is a hard shell on the outside of their bodies that doesn't grow as a spider grows, which is why young spiders molt as they grow bigger and outgrow their exoskeleton. Spiders are also, generally, very swift and can successfully flee a predator if not cornered.