Hi TiggerRabbit - Welcome to GameBoomers!!
Be sure of a few things: You must go up the Left-hand tree. If you put the feather in the correct spot, it turns orange and the Spider is attracted to it. That way, you can take advantage of the broksn part of the web, and get to the center. Knock out the spider with your sword when she approaches. That gives you time to pick up the skulls.
This web is easier than the first two; you just have to be sure you are in the right place.