What do sideswimmers eat?

"Sideswimmers" is not a recognized biological term. It's possible you're referring to a specific type of animal or creature, but without more context, it's difficult to determine what you're asking about.

Could you please provide more information about what you mean by "sideswimmers"? For example, are you referring to:

* A specific species of fish?

* A type of aquatic invertebrate?

* A fictional creature?

Once I know what you mean, I can tell you what they eat!