Just noticed these just under the top soil of my Juniper. (see picture)

Looks like maggots to me (when they hatch)?

As far as I'm aware these wont harm my tree, but I'm more curious as t how they got there, and what can I do to stop them coming back after treatment?

All advice appreciated.

If you think they will do no harm why do you want to kill them? It helps to know what country you are in.