Do y'all know if DE kills ticks? I believe an experiment is in order! It won't be hard to find some "guinea pig" ticks for it!
Yes, it kills ticks quite well. For our dogs, we would get some serious hand fulls and rub it all over the dogs body and fur, doing our best to get every one of the ticks we possibly could. We'd recheck weekly and re-apply as necessary. It worked beautifully and was significantly less expensive than the commercial medications.
We also spread a layer of it anywhere we found the ticks inside the house and they would slowly die off. The problem is that they can lie dormant for over seven years without any food sources at all, so it's always going to be a problem at some point or another. You can never truly get rid of them, but you can try to manage their recurrence.