Well, did you try to click on that LAST bug, the neon one? Noticed how, after you click on it, another bug lights up? Here's where it begins.
Click on that another bug. After you do, it lights up again, and after it yet another one. Repeat that, click on both of them. After you do, they both light up again, and after them a third one. Repeat that too, and in exactly the same order. Click that way on more and more bugs in the same order they show you. When you click on the last bug, they perform (flash all in their color randomly). Notice that order. Now you can use it on the mega-skull, and in one or two occasions later in the game again.
If that didn't help you, I call myself helpless
