Earthworms turn blue

[Otterwoman]

Can anyone tell me why sometimes my cut-up worms turn blue?
I cut up the nightcrawlers and feed them in the tank. Sometimes if I don't clean them up within a day, the cut-up chunks become bright blue in spots--almost a methylene blue color.

 

[Azhael]

This is just a wild guess, but could it be due to the degeneration of certain fats/oils?
I´ve seen that some of the earthworms i collect here (not sure of the species) have an iridescent "skin". When one of my dobrogicus puked one of these, it had an oily blueish colour.

Another wild guess would be that perhaps the blue patches are due to bacterial growth. Some bacteria grow in colourfull colonies.