I have a theory on this.

It looks like worms embedded in the skin.

That is common in some of the poorer countries, africa is the one place I can think of off the top of my head and I can't remember what the name of the worm is.

But on anyhand, it looks sort of parasitic - and by our very nature we are inclined to dislike the idea of any sort of parasite. We dislike anything that could make us sick, take over our bodies, change our thinking - because we are geared to LIVE. This is the same reason differences freak us out, because anything we see as different the brain often classes as Dangerous Until Proven Otherwise, in some cases like Phobia, that becomes completely wound tighter than it should be.

So i think in the long run, the reason this creeps us out is both that it is different and parasitic.