Not to cause more of a stir here, but I have found this thread extremely interesting, and just want to add my 2 cents worth.
We have, just this year, moved onto 13 acres. We have maybe 3 or 4 acres cleared, and the rest is HEAVILY wooded. Ticks were a horrible problem for us. We were all (including the kids) getting 3-5 ticks a week, no matter how we dressed, etc.
I would walk across the yard to put the chickens out, and come in to find a tick hanging off my leg. It was awful.
After seeing it here on BYC, we ordered a 50 lb. bag of DE (which BTW, will take us YEARS to use, lol). The hubby masked up, and spread it around the house, the kid's playgym, everywhere we we sat or were active.
We haven't had a tick in MONTHS. I use it in the animals' feed, no worms in the cats or dog, which are 100% outside animals. It makes huge anthills disappear. I use it in the coop and the chicken's dusting areas. The birds have no ticks, mites, etc., and as far as that goes, neither have the other animals outside, and the poor cats used to get INFESTED with them.
All the science in the world would not change my mind about how it works. My own personal experience has shown me that it works, and that's enough for me.
JMHO-
Jess