A good indication that this is a fallen world is the existence of insects that feed on human and animal blood. I would speculate that when God created the various forms of life it was a law that each group maintained itself by feeding on lower forms. Thus, plants absorb nutrients from the soil in which they grow, animals consume vegetable matter and humans can eat both meat and plants. I have left out carnivorous animals here but that is, as it were, a horizontal process. And it too may be the result of the Fall. Possibly there were no carnivores in the prelapsarian world or, if there were, they ate less evolved forms of animal life.
Be that as it may, bloodsucking insects are something else. We instinctively feel the wrongness of such a thing, and not just because they irritate us and spread disease. We recognise there is something unholy and corrupt about a lower form of life feeding on a higher form. One might even put certain bacteria and viruses into this category of lifeforms not created by God but instead being the product of the deforming of life by the dark forces and/or wrong human thought which has its effect in the external world, particularly in the deep past when physical matter was not as dense as it is now.
Obviously, the materialist will write this idea off as complete nonsense but it is a plausible theory from the spiritual perspective. God did not create mosquitoes and similar unpleasant creatures. They are either the creation of the created (a physical instantiation of spiritual misalignment) or diabolical perversions like the orcs Morgoth made from elves in Tolkien's world. For the sake of this post I looked up when bloodsucking insects are first thought too have evolved and the answer is about 150 million years ago which would seem to put paid to the idea. But life on this planet has been around for a lot longer than we currently estimate as the earlier forms existed when the Earth was less material than it is now so have left no trace. When God created the world he pronounced it good but it has gone bad and one of the signs of that is the existence of lower forms of life feeding on higher.
In Siberia there are myths that say the mosquito arose from the ashes or fragments of some giant creature or demon. Similar tales are found in North American myth, with the mosquito arising from the ashes of a man-eater, suggesting a common origin. It is accepted by many people that myths do point to genuine realities so perhaps here we have a folk memory of the fact that not all life forms were created by God/the gods but some are corruptions in a world gone wrong.