caterpillar

I have always wanted to raise a caterpillar into a butterfly because i think it would be cool and fun. But i cant find a caterpillar and i don't know where to get one and what it needs of course i can just look all of those up online but i wont know if its poisonous or not. I don't really know anything about a caterpillar except that it goes into a cocoon and turns into either a moth or butterfly. But of course i want the one i would raise to turn into a butterfly not a moth and when the butterfly would be able to fly i would let it go and if i liked raising it probably get another one. I think in some of my elementary grades some of my teachers raised caterpillars or some other animal or bug. It was pretty cool. So that's what Ive always wanted to do.