They look like black soldier fly maggots. Read the link below and see if that's what you have:

Here is a link that might be useful: Vermicomposting

In general nothing that grows in compost or in cold rot will harm your garden. You could easily make a case for eliminating grubs or perhaps hard segmented "worms" (I.E. things that turn into beetles), but these things you find are almost always interested in decay, not growth. Also, if this little thing is the only sort of compost denizen you find then the compost must be old. The number of creatures (mini, macro, micro and so on) in "fresh" compost can be wild!