The spikes might be gray or green or whatever to their nature, but colored red because of countless Critters landing on them and getting... spread out. Eventually, the critters learned to jump between the spikes and [the camera's placement] since the island is actually 3-dimensional, but the tunnels (and outer wall paths) are in general so non-wide that only forth and back matters.
That's my explaination. Then, why can't just Quote jump between the spikes and the camera? Um... I've not got a satisfying answer to this, but my primer is that he is too big to stay on the available ledges.
Butes are immune to spikes as well, BTW.