There's not just one in there though. This are about1 foot or bigger in size. I thought caterpillars would make a cocoon the size themselves? This would look like a entire family or so.
Testi is right. I can't remember what kind they are, but we get those here too this time of years. My Dad used to cut them out of our apple trees every year....along with a few choice words.
Yeah, they can get pretty nasty. I am told they run in cycles... some years there are hardly any, other years they are so bad you can't find a tree without some.
We always called them webworms but yes they are caterpillars. They will ruin certain species of tress and can spread quickly. Get rid of them as fast as you can if it's your property.
I lived on an acre and a half of land with about 30+ trees down in south-east Texas when I was growing up, and tent caterpillars were a very regular sight; they would even make nests in certain spots on the side of the house - but I don't remember them ever doing significant damage to the trees enough to kill them. The caterpillars themselves were pretty and harmless; I'd let them crawl all over my hands for hours.