I use a layer of compost as mulch, but every time I water, millions of tiny insects start jumping all over the place. Is it possible to identify them as I'm not sure if they're decomposing the organic matter or hurting the plants.
Sounds like springtails. Not a problem.
With one exception they dont harm plants, and eat bacteria, fungi, and decomposing matter.
The exception is the lucerne flea - but that lives on the branches and leaves.