Rabbi Yehudah HaLevi, in the Kuzari, discusses the harshness of life in the animal kingdom in the context of describing the wonder of its design:

"See how wonderfully conceived is the nature of the creatures, how many marvelous gifts they possess which show forth the intention of an all-wise Creator, and the will of an omniscient all-powerful Being. He has endowed the small and the great with all necessary internal and external senses and limbs. He gave them organs corresponding to their instincts. He gave

the hare and the stag the means of flight required by their timid nature; endowed the lion with ferocity and with the instruments for robbing and tearing. He who considers the formation, use, and relation of the limbs to the animal instinct, sees wisdom in them and so perfect an arrangement that no doubt or uncertainty can remain in his soul concerning the justice

of the Creator. When an evil thought suggests that there is injustice in the circumstance that the hare falls prey to the lion or the wolf, and the fly to the spider, reason warns him as follows: How can I charge the All-Wise with injustice when I am convinced of His justice, and that injustice is quite out of the question? If the lions pursuit of the hare and the spider of the fly were mere accidents, I should have to assert the necessity of accident. I see, however, that the wise and just Manager of the world equipped the lion with the means for hunting, with ferocity, strength, teeth and claws; that He furnished the spider with cunning and taught it to weave a net which it constructs without having learned to do so; how He equipped it with the instruments required and appointed the fly as its food, just as many fish serve other fish for food. Can I say anything but that this is the fruit of a wisdom which I am unable to grasp, and that I must submit to Him Who is called "The Rock Whose doing is perfect" (Deuteronomy 32:4)?" (The Kuzari, part III)

Rather than give an explanation, he states that since there is an a priori awareness that G-d created the universe and is just, and that animals are clearly designed to eat one another, then predation must therefore be planned, and it must be the product of a justice that is beyond our comprehension. Like the mystery of human suffering, the suffering of the animal kingdom is one of the ultimate, unknowable mysteries of creation.

Rabbi Avraham Yeshayah Karelitz, the "Chazon Ish" (1878-1953), gives more of an explanation, although one that is nevertheless still somewhat cryptic:

"Animals are similar to man in the structure of the body, with its aspects and capabilities; the material of their bodies is flesh and blood, sinews, bones and skin, and they possess a life-force. They possess senses like man, they sustain themselves like man, they are of two genders, male and female, and the difference of man from animals is in intelligence and language. Animals are of utility to man, such as an ox for a yoke and a donkey for a burden, and they prepare food for man, milk and eggs, and from some of them we obtain wool to wear, and some of them are themselves food for people. They were created as different kinds and as many species, and the food of each is different. People do not benefit from some of them, such as predatory animals, and snakes, and vermin, and insects; however they possess sublime necessity and benefit. Sometimes man is punished by way of them, and sometimes man learns wisdom and ethics from them. We are already used to their existence, and we feel that without them the world would be lacking, and the world is not beautiful and perfect except when there are predatory animals in it. The abundance of habit numbs the sense of wonder of the soul which befits every living creature by virtue of its being alive. As opposed to this, the soul does feel wonder from special species which are not so frequently found..." (Emunah Ubitachon 1:7)

Rabbi Karelitz seems to be saying that the harshness of nature, demonstrated by predatory animals, is part and parcel of the overall grand tapestry of creation. "We feel that without them the world would be lacking, and the world is not beautiful and perfect except when there are predatory animals in it." Mankind somehow intuitively understands that it is part of a greater good.

In summary, then, the essential answer is that such things are part of the larger picture, part of the greater good, part of G-ds ultimate and unknowable plan:

"For My thoughts are not as your thoughts, nor are your ways as My ways, says G-d." (Isaiah 55:8)