What is eating my morning glory leaves and stems and how do I stop it?

I planted morning glories outside at about 3 inches tall that had been starting from seed indoors. The plants finally starting taking off after a few weeks, and nothing bothered them, but recently something has starting chewing at all the leaves. The plants were finally starting to twine around the trellis I set up for them, and whatever eating them chewed off all the stems twirled around the bamboo posts! It only happens at night.

The leaves have holes similar to this http://i60.photobucket.com/albums/h22/lisa_s00/jun...

At first we thought it might be a rabbit, but we put mesh cages around the plants and theyre still being eaten every night, so we concluded it must be insects.

I know we have snails and slugs that hang around the garden, but some of the chewed leaves were far off the ground and I doubt the delicate stems of the plant would be able to support a snail or slug without snapping off the whole plant. There was also no evidence of any kind of trail that snails or slugs leave behind.

So my question is, what they heck could be eating my plants and how do I stop them? What are some natural repellents for whatever insects could be doing this.