Hey, to each his (or her!) own. I figured the water would be enough to keep them from getting in the mead. I haven't even bothered with airlocks on my last three batches.
It serves dual purpose for me, some of my carboys are hard to get to and it's hard to get the airlocks out to fill them, so it not only keeps the airlock liquid from evaporating so quickly, but also keeps things out if it should ever go all the way dry (only happened once)... but I did have fruit flies breed in an airlock and hatch on the wine side once. Only the once out of over 140 batches, but still not something I'd care to repeat.