No, Daphnia can not eat Hydra, Because the Hydra has tentacles to capture the Daphnia and eat it. The Daphnia therefore can not get free which means the Hydra can eat the Daphnia. The Hydra therefore has more force and can eat the Daphnia. Your answer is NO.
Daphnia eat algae so they are herbivores.
A better question would be, what fish don't eat daphnia? Seriously though, I've never had a fish that didn't like it, the same with blood worms. They will eat it whether its freeze dried or live.
As fast as they can.
The very predatory Hydra primarily feeds upon small invertebrates, such as Cyclops and Daphnia, that they pursue in the water.
Franklin Delano Roosevelt
Essentially zooplankton like Rotifers and Daphnia, Diaphanosoma. If they are quick enough, the occasional copepod but not usually.
Flake, Pellet, Tubiflex, Krill, Plankton, Brine shrimp, Blood Worms, Spirulina, and Daphnia
like small animals
Daphnia, or water fleas, are arthropods, more specifically crustaceans, like crabs, or krill!
Daphnia are primarily filter feeders and normally consume algae and small aquatic plants. While they may accidentally ingest microorganisms like fungi present in their environment, they do not typically seek out fungi as a food source.
Daphnia feed on organic detritus (tiny bits of dead stuff), if you are keeping them I suggest feeding them algae (grow in separate tank!), yeast or grain. Remember it is best to underfeed than overfeed otherwise you may kill them all.