This theory is actually pretty funny to me. I'm not even sure who exactly came up with the idea, but it's a little hard to believe. There was many different types of caterpillars when dinosaurs roamed the earth. Many where much larger than today. It's believed that they were just like insects and reproduced in vast amounts. There is proof that they have gone through several stages of evolution during the cretaceous period. Scientists pose that its very possible that caterpillars could have exhausted the plant life creating a high demand for food to all of the herbivores that habited the world back then. the conclusion is that the herbivores became extinct and the carnivores were soon to follow. The idea of caterpillars being the cause of the extinction of dinosaurs is a far cry from the truth though. Most people don't believe that this has happened.