Morality is about 'right conduct'.
By natural selection, organisms that have brains that react to living as a bad thing, or a neutral thing, die off and do not reproduce over time. If science agrees with this observation, then other scientific observations come into play to look at the energy efficiency of actions, look at the rate at which things can be eaten or used. I do not see how one can be concerned about any other behavior except in relationship to ourselves. We are always in the picture, otherwise we are dead and not reacting. Your example of the spiders that eat each other in the business of reproducing - if it works for the spiders, then it works for them, is good for them.