Another thing about the importance of parasites and other “pesky” organisms is that they are a non-stop irritation to almost all other animals on the planet…..and the impact of that cannot possibly be overstated. It affects EVERYTHING those animals do. It even affects what they look like and how they’re shaped. The clouds of biting midges breeding in a marsh are going to affect how long an animal stops to graze on wetland greenery and how much of that greenery it takes. Explosions of mosquitoes that follow a wet season are what drive larger herd animals to seek drier prairies and meadows, allowing a completely different set of animals and plants to surge. Population booms of ticks and lice drive animals to practice mud-wallowing, social grooming, population splits and even mass migrations. Flies are the entire reason zebras have stripes. These are just a couple of examples, but basically the whole face of our planet looks the way it does because some of the tiniest animals are constantly pissing off the largest.
Oh I thought the zebra thing was more widely known! It was only really figured out in the last few years though. https://www.sciencemag.org/news/2019/02/zebra-stripes-confuse-biting-flies-causing-them-abort-their-landings
One experiment basically just dressed up regular horses as zebras with different stripe patterns and densities. All of them still attracted flies from afar, but once the flies got close, they had difficulty figuring out where to land. They don’t mention this in the article, but flies look for whatever “stands out” in their field of vision, in fact it’s the reason why even non-biting flies will circle around your head. Finding an animal to bite means investigating either dark blots in a lighter landscape or light blots in a darker landscape…but then what do you do when you reach your destination and it’s just alternating fields of stark black or white? The flies, I think, probably get confused because their brains are trying to denote either the black or the white stripes as empty, surrounding space. This is so effective, that the solid color horses had up to 60 flies land on them every half hour, but the zebra cosplay horses had as little as four or five!
This is also almost definitely why human beings in those same environments paint stark white stripes on their dark skin, though I’m not sure if that became a tradition whose original purpose was forgotten, or researchers simply didn’t find a way to just ask.
