Fish:
* Bass (largemouth and smallmouth)
* Crappie
* Sunfish
* Trout
* Pike
Other aquatic insects:
* Dragonflies
* Damselflies
* Larger water boatman species
Amphibians:
* Frogs
* Toads
Birds:
* Herons
* Ducks
* Kingfishers
Mammals:
* Otters
* Muskrats
Reptiles:
* Snakes (especially water snakes)
It's important to note that these predators don't exclusively eat water boatmen, but they are a common food source for them. Greater water boatmen are also prey for many other animals depending on the specific location and ecosystem they inhabit.