The Northern California Fly Fishing Board

Hi All,
First time member with a question. I was fishing the Stanislaus just below the dam last week and watched nice trout slurping and slapping at a tiny emerging bug in the film. This went on for 4 hours. The most prolific bug I could inspect in the film was about a size 24, with a dark green body and a translucent to white wing about the length of its body. It's feet were those of a crawler. Nothing in my fly box looked similar and I had few that small. I did manage to fool 2 trout on a caddis poopah but couldn't match the hatch. Any suggestions as to what the bug was and what flies might have enticed them. Thanks.