They would say He didn't that it is a mutation as a result from the fall from perfection...just like the leech was not supposed to suck blood or animals tear each other to pieces...it is all as a result of the fall from grace.
You can't reason with them on subjects like this.
A flower blooming after a land decimated by a natural disaster is a sign of beauty and shows God's wonderful nature but the blood-sucking creature that lays eggs inside another animal where its young eat from inside out and kill the creature is a result of Satan and the imperfection introduced along with the unnatural effect of the environment.