Feeding fish is a good source of protien however, if it's too big for the fish to swallow, it will kill the fish. Maggot can live for quite alot of minutes underwater and it takes less time for it to chew through flesh.
I fed my goldfish maggots from a tackle shop and nothing happened. This fish should kill the maggot in it's mouth otherwise it would just chew through it's stomach. Check for uneaten ones though because they can cause serious harm to water once they start rotting and turning brown.
Also, don't forget they cawl under the gravel or into sand.
I just fed one at a time so I could keep an eye on it.
And don't forget that people fish with maggots and would no doubt be a food source for a huge amount of fish in the wild.
Make sure they are clean though.
And I would just like to add, maggots arn't dyed, its their natural colour. Its the species they are.