Whenever it rains at night, the outside of my exterior garbage bin gets covered with white wormlike creatures, about 1/2 to 3/4 inch long. I think they may live in the bottom of the garbage on a regular basis, although my wife failed to get rid of them by pouring large amounts of ammonia into the bin.
Given that it’s in (or on) the trash bin, it’s likely to be fly larvae of some sort. But if you have trees overhanging your storage area, it could be beetle larvae that are being rinsed off the leaves.
At >1/2" inch? Not chance. Fruit fly larvae only measure about 1/4". These will be ordinary house fly maggots.
You won’t get rid of them with ammonia because flies lay new eggs all the time. If you really want to elimiate them You should try to get hold of one of the Dichlorvos based insecticidal pads and put that in the bin with a good lid.