What are mosquitoes good for? That depends on what kind of critter is answering the question! Ask my goldfish and they would say that without the mosquito larvae I give them as treats, their lives would be dull and lifeless. Ask many freshwater fish living in small ponds in mosquito areas, and they would say they depend on mosquito larvae for food (if they could talk - most can't).
Frogs would say mosquitoes are good for eating too, as would a large number of birds and bats. Many flowers might tell you (if you knew how to hear them) that mosquitoes are important pollinators for them. In fact, while it may seem that mosquitoes live mostly on human blood, they actually live mostly on nectar. Only the female needs a feed of juicy blood, and only then when she's about to lay her eggs.
Mosquitoes do suck blood and transmit diseases because of their unfortunate habit of occasionally feasting on blood, but only a few of the mosquito species are of any major concern. The major diseases transmitted by mosquitoes include Dengue fever, encephalitis, malaria, and Ross River virus. They can also be a damn nuisance if you are outside trying to enjoy a barbeque, or inside on a humid summer evening trying to get to sleep.
Mosquitoes belong to the same family as flies (Culicidae). They have six legs and two scaly wings. The mosquito has a big nose called a proboscis which protects its piercing and sucking mouthparts. The mosquito larva is aquatic and much admired as a treat by fish and frogs. The adult is terrestrial and most stay within two kilometres of their original breeding place. Some never stray beyond a few metres from the place where they were born.
The female mosquito lives about three weeks, but the male has an even shorter lifespan. They mostly feed on nectar and other plant material, but when the female is developing eggs a good blood meal is required for protein. When the young hatch, the young wrigglers are aquatic and eventually develop into pupae (tumblers), which are comma-shaped and which emerge as adult mosquitoes.
So, what are mosquitoes good for? While many humans might say that mosquitoes are good for nothing, they actually have an important role to play in the web of life. Like all other creatures, they are part of this web and have as great a part to play in the life cycle as any other creatures. Looked at under the microscope, mosquitoes and their larvae are beautiful and complex creatures and like all other creatures they have their place in nature.
Every creature has its place in the web of life, and mosquitoes are no different. They have place in nature too.