Probably it's from flea beetles - a number of different small, black beetles that jump off and hide when disturbed, hence the name. I have had fair luck dusting teh plants and the surrounding soil/mulch fairly heavily with Diatomaceous Earth. You do have to re-apply after any rain, and after watering if from overhead. I find DE works best if applied while the plants are slightly damp, and heavily enough that they look ghostly. As you say, once the plants are above a certain height, the problem goes away.

You may find DE at a garden store or big box store (Lowe's carries some sort of DE locally), otherwise, Peaceful Valley carries it. DO NOT get the kind sold for pool filters, as it has been heat treated and has lots of small particles of silica, so is VERY bad to breathe. Regular DE isn't great to breath, but.....

I agree it sounds like flea beetles. I grow a lot of eggplants (love em - this year I'm growing five kinds) and flea beetles love em as much as I do.

Two schools of thought on them:

1. Paul James (Master gardener, organic) believes that many "bad" bugs really don't do that much harm other than beauty wise. Flea beetles, acc. to him, kind of fall in that category. My experience since hearing him say that is to just let them enjoy the leaves, and I don't lose any fruit. The leaves look lacy, but the plants stay healthy and still bear plenty of blemish-free fruit.

2. Companion planting. This year, I'm gung ho on companion planting and have read Sally Jean Cunningham's work on the subject again and again. There are plants that supposedly will repel the flea beetles and/or act as a "trap" crop.

Radishes, for example, are a flea beetle favorite, and you can plant radishes around your eggplants (and beans). The flea beetles will go for the radishes, and when one gets infested, pull it up and toss it. (Into the compost pile? I plan to if it's heating)

To repel flea beetles: mints and catnip. Since both are invasive, what I've done is put a few pots of both around my eggplant areas. Just finished potting those up today in fact.

I've got radishes planted throughout the garden, because they're supposed to repel cucumber beetles as well.

Disclaimer: the companion planting stuff is what I've read only. I'm only now trying it, new this season. I'll be reporting back in the fall on how well it all worked. But I'm very optimistic.

D. earth is good stuff too, but remember it can also kill beneficials. Any hard bodied bug.