a lot of herbs are, to varying degrees (rosemary is in a lot of the bug repellent mixes, as are some geraniums, and many citrus-scented things), but it happens that this particular variety of thyme is heavy on the stuff that makes citronella citronella, so you can rub some on your skin or just walk through it (groundcover thyme does pretty well with being stepped on, within reason), and release the chemicals that a lot of bugs avoid. I figured it was worth a shot, since I'll be standing out there to harvest eventually. You can also cook with it. ;) mmm...citrus thyme.
I can get you the exact scientific name, if you like.