Why is my Cat Throwing up?

Hey, could be anything. I'd get him to a vet as soon as you can, and have them test a fecal sample for parasites as well. Vomiting is a symptom that has a huge range of causes. Generally if the pet has eaten something bad (like the wasp) it should have passed through them in 12-24 hours, but it's possible that the wasp stung him somewhere inside and is now irritating him. That's just a wild guess on my part though, like I said, could be a very wide range of issues that you would not be able to diagnose without a veterinarian.