Wouldn’t it be great if you could download an app onto your smartphone that would keep mosquitoes away? It would be, and there are plenty of apps you can download, but don’t expect them to work. These apps (one of which actually claims to be a prank you can use on your friends) are a new version of the small, inexpensive devices that supposedly repelled mosquitoes by emitting the same sound as a flying dragonfly. Dragonflies are mosquito predators and so, theoretically, the sound of one approaching would cause mosquitoes to flee. In other cases, the sound is supposed to imitate a male mosquito’s mating call. You might not think this would work as a repellent, but consider that only female mosquitoes bite, and only when they have fertilized eggs to lay. Again, according to the theory, female mosquitoes with fertilized eggs don’t want male mosquitoes around them and so will leave the area when they hear one.