Why do mosquitoes exist?

There are about 3,500 species of mosquito, and only a few hundred bite humans. Males and many females feed on nectar, pollinating plants in the process. Mosquito larvae are a major food source for fish, frogs and aquatic invertebrates, while adult mosquitoes feed bats, birds, dragonflies and spiders. In the Arctic tundra, huge swarms emerge in summer and can influence caribou migration routes. Despite these roles, mosquitoes also transmit diseases like malaria, dengue, Zika and yellow fever, killing more people than any other animal. Some scientists debate whether eliminating specific species like Aedes aegypti would significantly harm ecosystems.