Water boatman is not a man, it is a water bug that have legs that they use to paddle on the water like a boatman does with oars.
Due to their size, they are only eaten by bigger
fish with mouths big enough to eat them. Supply of water boatmans is not consistent,
so you may have to order them from fish farms. If you like to collect wild
plants from nature and you are worrying about pests(including mosquito larva),
water boatman will hunt them down!