I just found them, hopefully in time. Just another place to look for the larvae. I drained the water and then added a small chunk of mosquito dunk to each water basin. Mosquitos suck!
They sure do - figuratively and literally! That's why I don't use those containers. I'm always dumping wigglers out of the ones at my Mom's house. But I certainly understand that not everybody has the time or desire to spend time watering every day, I'm not knocking their use. Instead of spending money on the dunks, and if this is physically possible, dumping the water out every 5 days can prevent having any wigglers reach maturity.
I put a piece of nylon pantyhose over the opening, so the bugs can't get inside and start breeding. It seemed to work.