... the "mosquito fish."  (AKA: Gambusia Affinis.)

image courtesy: wikimedia commons

It can apparently eat up to 500 mosquito larvae a day and give birth to up to 60 little gambusians a month while surviving adequately in oxygen-depleted water. That is, environments similar to those stagnant swimming pools and back yard spas on properties left vacant in a foreclosure; great breeding grounds for mosquitos-borne diseases, like West Nile virus. (Source: WSJ.)

But, this idea may ultimately be all wet. It's a great idea on the surface, but I wonder... who takes care of the little critters after all the mosquitos are gone?  And, when the water starts to dry up, I imagine the backyard would start to take a uniquely odoriferous aroma.