I feed some to mine every few weeks, the fry especially seem to love them. Just note that rainwater isn't always the best for your tank, lacking the essentials that dechlorinated tap water provide. I like to catch as many as I can and place them in the water during changeover.
What would everyone's best advice be for catching them? It can be a difficult process and waste quite a bit of rainwater.
the best way to get the most and keep your rain water is to get like a old pair of your nanas tights and run the water through that this will catch wat eva is in the water do this ova another bucket so all the rain water gathers in the other bucket so you can keep it and wen you have your moquito larve in your tights feed them to your fish discarding any little critters that shudnt b in there.