Oh, your post is soooo timely! I was looking out at the back corner of my yard....I'd planted some wildflowers back there a couple years ago and they've not returned. And I thought, "Oh, wouldn't daylillies be lovely back there?"
Guess not! I knew they reproduced at a pace that rabbits would envy, but had no idea it was a plague! Best of luck in your battle!
If you're a good gardener--which I'm not--they are actually pretty easy to care for. The thing with daylilies is that you MUST divide the bulbs at least every two years, preferably every year. We went eleven years without dividing.
Live and learn!