Wonder why this isn't in the Religion and Philosophy category.
Morality is subjective the the perception of the species. Hindu's say eating meat is immoral. Christians eat meat. Who's right? If black widows had large brains and could conceptualize morality, they may see it as virtue for the female at eat the head of the male after breeding, as it's in their instincts to do that.
As a community species, we base our morality on what is beneficial for a societal species and the question of suffering. The morality given in religious books is usually far from moral, except on a few guidelines which span all faiths.