I will place verses to ponder on:
If you do not let my people go, I will send swarms of flies on you and your officials, on your people and into your houses. The houses of the Egyptians will be full of flies; even the ground will be covered with them. - Exodus 8:21
Then the Lord sent venomous snakes among them; they bit the people and many Israelites died. - Numbers 21:6
He said, “If you listen carefully to the Lord your God and do what is right in his eyes, if you pay attention to his commands and keep all his decrees, I will not bring on you any of the diseases I brought on the Egyptians, for I am the Lord , who heals you.” - Exodus 15:26
See now that I myself am he! There is no god besides me. I put to death and I bring to life, I have wounded and I will heal, and no one can deliver out of my hand. - Deuteronomy 32:39
Even from the very beginning God set forth a command in the Garden of Eden for Adam and Eve:
Now the Lord God had planted a garden in the east, in Eden; and there he put the man he had formed. The Lord God made all kinds of trees grow out of the ground—trees that were pleasing to the eye and good for food. In the middle of the garden were the tree of life and the tree of the knowledge of good and evil... The Lord God took the man and put him in the Garden of Eden to work it and take care of it. And the Lord God commanded the man, “You are free to eat from any tree in the garden; but you must not eat from the tree of the knowledge of good and evil, for when you eat from it you will certainly die.” - Genesis 2:8-9, 15-17
For me, there is another reason God put these creatures on Earth:
We are here for only a moment, visitors and strangers in the land as our ancestors were before us. Our days on earth are like a passing shadow, gone so soon without a trace. - 1 Chronicles 29:15 [testing ground]
I applied my heart to seek and to search out by wisdom concerning all that is done under the sky. It is a heavy burden that God has given to the sons of men to be afflicted with. - Ecclesiates 1:13 [trials]
I have seen mortals weighed down with a burden that God has placed on them. - Ecclesiastes 3:10 [trials]
Be glad about this, even though it may now be necessary for you to be sad for a while because of the many kinds of trials you suffer. Their purpose is to prove that your faith is genuine. Even gold, which can be destroyed, is tested by fire; and so your faith, which is much more precious than gold, must also be tested, so that it may endure. Then you will receive praise and glory and honor on the Day when Jesus Christ is revealed. - 1 Peter 1:6-7 [trials]
Every test that you have experienced is the kind that normally comes to people. But God keeps his promise, and he will not allow you to be tested beyond your power to remain firm; at the time you are put to the test, he will give you the strength to endure it, and so provide you with a way out. - 1 Corinthians 10:13