Puking... but due to you words I can translate now from Dutch from the official waterbirdorganisation.
Roundworm. (Ascaridia galli). Looks like spaghetti and an adult is 5cm long. They lay eggs, that come out through poo. The eggs are not contaminable yet, they have to be larvea first. Warm tempures (20-25 degrees) make the larvea come out. In ducks, due to the tocis juices in their intestines; the eggs brake and the larvea come out of the eggs in their intestea. Where they grow to adult worms. Hence you might see them in their poop.
Small roundworm. (Heterakis gallinae). This small variant does not cause disease unless with many. They are more resistant to the duck temperature. And after 5-8 weeks after infection the eggs leave through poop.
Hairworms. (Capillaria). Can cause really bad disease, but are not seen by the naked eye. 0.1 mm thin, 1-3 cm length. They live in the small intestine. after 21-28 days they lay eggs. Cause many damage.
Small and big tapeworm. (Raillietinae and Davainea proglottina)
These are segmented worms and look like rubber bands. Big ones can be 15cm long, small ones 2-4 mm and barely seen with the naked eye. The small one brings really bad diseases. Snails are temporary hosts.
Gapeworm. (Syngamus trachea).
They live in the throat. Sometimes you can see them. The ducks can swallow the eggs and poop them out. Ducks will yawn, shake their head, gasp for breath, become thinner, and die.
Damage to Ducks:
- They don't get any nutritions and slowly get food-deprived.
- Their intestines get dammaged, this leeds to diahrea and lack of nutrition.
- These worms have toxic poo (small tapeworm)
- They fill up their intestines and block them (roundworm).
Ducks get lethargic.
Do I need to de-worm my ducks regularly?
No. Ducks need these worms in a tiny amount. If they have them in a tiny amount they make antibodies for them. If you de-worm them more then needed they can't make these anti-bodies. Only de-worm them if a duck gets lethargic, while eating properly. Or when they are going to lay eggs and raise the ducklings naturally. Ducklings do not have anti-bodies to these worms.