Morality is a human construct. Nature has no morality, only survival matters - by any means. That's why such cruelty (from human moral viewpoint) is found in Nature.
But perhaps it does? Animals kill other animals only to survive (to kill them in order to eat them or to defend themselves from being killed/eaten)
Humans may be the only species who hurt other humans just for the fun of it - now _that_ is cruelty.