What is the Most Effective Killing Machine Ever?

The answer is unsurprising, but, by me at least, unexpected. Mosquitoes:

Researchers estimate that mosquitoes have been responsible for half the deaths in human history. Malaria accounts for much of the mortality, but mosquitoes also transmit scores of other potentially fatal infections, including yellow fever, dengue fever, chikungyunga, lymphatic filariasis, Rift Valley fever, West Nile fever, and several types of encephalitis. Despite our technical sophistication, mosquitoes pose a greater risk to a larger number of people today than ever before. Like most other pathogens, the ciruses and parasites borne by mosquitoes evole rapidly to resist pesticides and drugs.