I run a couple deck ponds, up on a shelf so
I have a good look at what is inside - snails,
tadpoles, seed shrimp, tubiflex worms and other
assorted critters.
One thing I noticed was that in a tub that only
had snails I never got any mosquito larvae.
A tub right next to it, without snails, I got larvae.
I figure the snails slurped up the eggs along with
everything else. Sometimes you'll see a snail
crusiing across the water, upside down, seemingly
vaccing up the surface,

I use Mosquito Bits in pondlets and areas that I'm
not keeping a close eye on.

k :-)
http://tinyurl.com/6bguh ~ new pond keeper info
http://tinyurl.com/yp64db ~ slide show of pond