So Christian theologians of all stripes have to face the challenge posed by animal pain. Here recent studies in biology have provided surprising, new insights into this old problem. In his book Nature Red in Tooth and Claw: Theism and the Problem of Animal Suffering, Michael Murray distinguishes three levels in an ascending pain hierarchy (read from the bottom up):

Level 3: a second order awareness that one is oneself experiencing (2).

Level 2: a first order, subjective experience of pain.

Level 1: information-bearing neural states produced by noxious stimuli resulting in aversive behavior.

Spiders and insects—the sort of creatures most exhibiting the kinds of behavior mentioned by Ayala—experience (1). But there's no reason at all to attribute (2) to such creatures. It's plausible that they aren't sentient beings at all with some sort of subjective, interior life. That sort of experience plausibly does not arise until one gets to the level of vertebrates in the animal kingdom. But even though animals like dogs, cats, and horses experience pain, nevertheless the evidence is that they do not experience level (3), the awareness that they are in pain. For the awareness that one is oneself in pain requires self-awareness, which is centered in the pre-frontal cortex of the brain—a section of the brain which is missing in all animals except for the humanoid primates. Thus, amazingly, even though animals may experience pain, they are not aware of being in pain. God in His mercy has apparently spared animals the awareness of pain. This is a tremendous comfort to us pet owners. For even though your dog or cat may be in pain, it really isn't aware of it and so doesn't suffer as you would if you were in pain.