No, no need to feed - they are living off by-products of your system. If you want to increase their numbers, you could try feeding your tank more of whatever you normally feed and watch to see that nothing else out competes them as a result. -Also theoretically you could change the balance if you were to add a coral or LR to your tank with critters that would out compete them (or even eat them, I suppose)
If the status quo continues to increase their numbers, it might be wise to harvest some every 4-6 months.