Ducks eat worms and other insects like most birds
yes i think that is how it goes in a ecological pyramid.
Spiders and praying mantis do.
there isn't an insect who feeds on fishes.
Owl
A duck that eats fish is known as a "dabbling duck." These ducks primarily feed on plant matter and small invertebrates but may also consume fish occasionally. An example of a dabbling duck that eats fish is the Northern Pintail.
The duck will get sick
raccon
The nightingale eats spiders and ants.
a lizardfly
grasshopper
Owl
Yes the puma could choke on the duck's bill or the duck could give the puma mercury poisoning after it eats the duck.