lily beetles

This is the dreaded lily beetle, scourge of the garden. It's only about a quarter of an inch long, but it has friends. Lots of them. And together they do grievous damage to my beautiful lilies. Asiatic lilies seem to be hit the hardest. These guys lurk on the ground in the early spring, waiting to pounce on the greenery as the first leaves push out of the ground, and they don't quit till frost comes around again in the fall. And their babies are worse. The adults lay eggs on the underside of lily leaves. The hatchlings have a brilliant way to hide - they cover themselves in their own poop, so that birds won't recognize them as prey.
I waste a lot of time picking them off and crushing them or dumping them into a dish of soapy water. If I return to the plant I cleaned off an hour ago, more have moved in. Some people I know have become so frustrated, they have yanked out all their lilies. But that is blaming the victim, don't you think?
I had a brain wave the other day. I brought home a lovely bag of coffee grounds from those nice people at Starbucks. I decided to conduct an experiment. I scattered coffee grounds over every lily head, making sure lots ended up where the leaf meets the stem, which coincidentally is where lily beetles most like to hang out. Will this keep the bugs at bay?
Now, 24 hours later, I checked the lilies, and the bugs are only on the plants where the coffee was washed off by rain.
After doing some reseach on the internet, I'm confused. Some sources say coffee grounds are a valuable source of nitrogen, magnesium, and potassium, are great for acid-loving plants, and make great compost. Other sources say beware - our soils on the east coast are already acid, and coffee grounds make the soil even more acidic. Plus, pure coffee in a thick layer on the soil encourages the growth of mould.
I'll keep the observations going for a while, and report back.

The picture below shows what lily beetles do best - chew holes in lilies and make baby beetles.