I live in an area where we have these[1], and they're generally not something you see all that often. Their biggest danger isn't their venom (they're less venomous than the diamondback) so much as their curiosity, which can get them into locations they otherwise don't belong. They aren't overly aggressive snakes, and I've encountered them several times over the years.

Alon with bullsnakes, they're extremely useful for getting rid of said rodents—which CAN carry awful pathogens, like hanta virus!

[1] https://en.wikipedia.org/wiki/Black-tailed_rattlesnake

Venomous snakes far outnumber the poisonous ones.

Lots and lots of delicious ground-dwelling birds eat ticks (Turkey, Chicken, Quail), but they'd figure something else out.

I’ve seen researchers suggesting that mosquitoes aren’t a big enough part of anything’s diet to be missed:

https://www.nature.com/articles/466432a

The serious proposals to eliminate mosquitoes only propose to eliminate the mosquito species that carry nasty human diseases. If those species were eliminated other mosquito species would quickly expand to replace the eliminated species.

So that's good for the birds, and bad for the humans that want to get rid of all the pesky annoying mosquitoes, not just get rid of mosquito born disease.

Yes, all the ectoparasites, look it up. We've eliminated most endoparasites that used to live inside us. If we figure out how to, we should eliminate the ectos, including mosquitos.

Jellyfish blooms actually are an ecological issue in some places. They thrive under certain conditions and wreck fish populations.

As I understand it, scientists believe that lobsters are also functionally immortal, just not invulnerable. I think the problem is that after a while, it takes so many calories to continue molting, they simply can't hold enough in their bodies or something? Anyways, they don't have an old age problem like you'd expect.