It's just like Nixy to follow Timby on some sort of personal errand of a deeply mysterious nature - out of sheer curiosity and probably without discussing it with Timby - only to run into trouble. It should have served as an early warning for him when Timby's every move only further kindled Nixy's curious sense, but we wouldn't want to put an old adage about cats at too great a risk, now would we?
As for why gathering bugs (or whatever about Timby the absence of which in Nixy so set off our cryptic furry friend) qualifies as "protection" from Fifi, we are unsure. It may not be that Fifi is peckish for the gruesome critters; it may be that he wants his precious wooded grounds rid of them. But it also may be an arbitrary measurement for who is & who is not allowed to stay - a measurement that finds its origins in a mind beset with madness.
It may even be that Fifi considers anyone who wears a monk's habit and gathers bugs in the forest unworthy of the trouble to chase them away.
"So, uh ... I have to ask:
"... Why are you gathering bugs in the forest?"
"Ssh! It's to appease Fifi."
"You didn't come to Fifi's woods without protection, ... did you?"
"Ssh! Here he comes now!"
"Yip yip!" BANG!