The answer is they breed and lay eggs in water. I mean they can use a drop of water to do this the little buggers. Now this year, especially here in CO it has been really, really wet. There are puddles everywhere. These mosquitoes will leave there children in the smallest puddle and they will cause havoc to us humans not to mention those other beasts who do not even have hands to swat them. Pray that it dries out a little so they'll go away. If it does continue to rain then invest in deet stock, it will be a good investment this year.