It’s also accounted for almost 100% by mosquitos, specifically the diseases they carry…so not really the mosquitos at all. Quick searching shows snakes following mosquitos with 100,000 deaths caused per year. In any case, the scale is prodigiously unbalanced. Human animals kill trillions of non-human animals, almost entirely for their own pleasure. Non-human animals kill a few hundred thousand human animals (or a bit over a million if you count mosquito-borne disease) in self defense or by accident.

Hills are why bikes have gears and there are plenty of chilly hilly places with strong bike infrastructure and culture. Not Just Bikes goes off on this subject frequently. Check them out on nebula or youtube for a laugh and some good information.