Mosquitoes actually are not replaceable in any ecosystem that naturally has them and that includes replacing them with any of the non biting species because these are the traits that make them so core to food webs:
Tiny
Can use every single pool of moisture to raise generations no matter how dirty and stagnant and low in oxygen
Can fly
Males get by on just sugars
Females take protein from larger animals to manufacture thousands more eggs
All these things combined allow thst ecosystem to make huge volumes of insects from conditions barren to most other macroscopic life. You might think there are other insects that seem to make huge massive swarms out of nothing but there's really nothing that hits all the same qualities *except other insects that also suck blood.*
It's the precise combo of being able to "prey" on things millions of times larger and breed in nothing but a few drops of filthy rainwater or the moisture in a rotten log. That's the most efficient combination for anything that size to multiply that rapidly where nothing else can even survive, except of course the things that can move in because they eat them :)
A lot of people ask "could they just not be itchy though?" and I regret to inform that isn't actually their doing, there's no evolutionary advantage to making you itchy. That's your own body detecting the intrusion of another creature's saliva into your skin, where it doesn't belong, and reacting with histamines.
If you've ever been bit hard enough by a cat, dog or even human you may notice a similar effect!
I remember having a conversation with someone about my hummingbird banding volunteering and how the data went toward support for conservation efforts among other things.
They were all for that, and loved hummingbirds and supported it!
And made a quip about how the only thing they wanted to see extinct were mosquitoes and small biting insects/fruit flies.
40 to 60% of a hummingbird’s diet, and their main source of other nutrients, is small, soft bodied insects.
Including mosquitoes and fruit flies.
They had a massive struggle not wanting to accept that no fruit flies and mosquitoes = no hummingbirds.
Bluebirds also eat tons of mosquitoes!
I've also added this on other big threads about this topic but I should add it here: Being INCREDIBLY OBNOXIOUS to larger animals, even when they aren't spreading any pathogens (and again, most mosquitoes don't!) actually is another vital purpose. Ecosystems need biting and stinging things to keep big, stompy, hungry beasts from getting too cozy. Mammals are the most resource-hogging animals in almost any biome but parasites can inhibit their growth a little (a good thing), discourage them from spending as much time in the same area or ward them away from whole areas to begin with. Mosquitoes in particular breed in filthy, stagnant bacteria-rich water. You know what leaves behind conditions like that? ANIMALS! Animals eating all the plants, wallowing in the mud and shitting everywhere! A herd of ungulates can turn a lush and healthy marsh into just a cesspit if nothing stops them. But it's mosquitoes that find a cesspit an appealing nursery. And then you get a cloud of mosquitoes so dense that the ungulates move on! There used to be a great BBC documentary that actually showed "mosquito season" driving a mass migration of African megafauna but the shittified search engines right now are only showing me articles about mosquito control no matter how I try to find this again, gee thanks, maybe someone else can find it? So while the "mosquitoes are bad" all the big animals leave for months. Months of the plants growing back, months of the water clearing up until it's drinkable again (and the mosquito larvae themselves are filter feeders!), months of the mosquitoes becoming food for tiny birds and lizards and arachnids and amphibians, and the beautiful wetland is back again strong enough to survive the repeat of that cycle the next year. Everything you hate in nature - the ticks, the territorial wasps, the stinging plants - are pretty much nature's immune system. Obviously this doesn't mean the big mammals are "bad" either. The cycles of destruction are themselves also something ecosystems come to rely on as a regulatory force :)
