(CNN)Not all mosquitoes are created equal, even if it feels that way when they bite you.
There are about 3,500 species of mosquitoes around the world, but only a few are responsible for spreading infectious diseases to humans.
Among those mosquitoes that are thirsty for human blood is the Aedes aegypti, which is the primary spreader of yellow fever, Zika virus, dengue and Chikungunya virus.
But how did Aedes aegypti mosquitoes evolve to specialize in biting people? New research published today in the journal Current Biology has revealed that two factors play a major role: dry climate and city life.