The question as to how far down consciousness goes is still a matter of debate. The idea that consciousness goes all the way down, i.e. to rocks et al. is called panpsychism in philosophy. I don't think that's likely, since our best bet is that consciousness is maybe/probably an emergent property of information processing in the brain. How complex that information processing has to be to result in consciousness is an interesting proposition, and could be hard to determine given the subjective nature consciousness to begin with.
Still though, I can't imagine experiencing consciousness, responding to stimuli the way I respond to stimuli, and thinking that animals/bugs that also respond to stimuli in the same manner as we do are not conscious. The fact that this assumption has permeated culture throughout history seems like a very obnoxious oversight and has probably led morally sane people to enact morally insane abuses towards animals and I think that is a shame.