Beetle Larvae
This includes the larvae of various beetles which live in freshwater. The larvae are the child version of the insect, before it transforms into an adult - like a caterpillar changing into a butterfly.
Beetle larvae in the pond look a bit like dragonfly, damselfly or mayfly nymphs but beetle larvae only have two tails and they don't have gills along their body. Like their adult versions, they tend to be voracious predators which can move quickly through the water to pounce on their prey.