The first picture and inset are images of a Bloodworm, the larva of the midge. Bloodworms are easily spotted because of their bright red color. The second image shows the final stage of the pupa. When the metamorphosis reaches this stage the pupa must find dry land - the ground, a rock, a floating leaf - so the adult can crawl out of its protective shell. The third image shows the perfectly formed outer shell that's left behind after the adult breaks out. When the fly emerges, the dry wings unfold and the midge is ready to fly off, leaving behind a perfect mold of itself.
If you come across a large infestation of bloodworms, usually in your filter, collect them and feed them to your fish. Don't kill them, as many folks are prone to do because they don't understand what they see. Your fish will love you for it. Fish usually go "bonkers" over live food and blood worms are a favorite.
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