It appears that Spidermonkeys don't keep track of their trees and will continue to spread throughout the entire deep rain forest biome the longer a Hamlet world exists. Not sure if it has to do with saving and quitting the game, length of time the world has been active, or world hopping but regardless it's something that gets annoying, lowers frame rate, and I am pretty sure it wasn't intended.
Steps to Reproduce
Have a Hamlet world that exists for a long time and either save and quit a lot or world hop a lot. That said, if a cap was put on the amount of spidermonkey that are allowed to exist in the world (not sure how hard this is to do) that might be an easier fix...
This issue has not been confirmed by a developer yet.