Using diatomaceous earth for insect killer

My understanding is that diatomaceous earth needs to stay dry to be effective. When wet it clumps with soil particles and can't be inhaled by insects. It works by acting like many microscopic bits of broken glass which damage insects breathing anatomy.

Yes, it needs to stay dry. It is great as an indoor/basement/garage insect killer though. It is mostly harmless to pets and humans, as long is it isn't inhaled. So if you have small pets or toddlers, I wouldn't use it indoors.

Several years ago, we had two dogs and the fleas were really bad in our area. We had a large crate in the basement where they slept at night, and we got a bad flea infestation down there. I treated the yard, treated the dogs, but fleas are cannibalistic in that they will try to survive off of dead fleas, so they can be hard to get rid of. I tried bug bombs, sprays, even the bug bombs for bed bugs, since they are supposed to be more effective on fleas as well. None of it seemed to totally wipe them out.

I finally read about DE and spread it all over the basement, and didn't let any animals or people down there for about a week. I hit everything with the shop vac to get the DE up and any dead fleas and eggs, and then applied it again. After two treatments, letting it sit for about a week each time, they were finally gone. It isn't a direct killer, but as they move across it, it scratches and irritates them and they finally die off.

For outdoor use, Bifen has been great for us. It gets mosquitos, spiders, termites, fleas, ticks etc. I use a two gallon garden sprayer and hit all the bushes and grass out back about every 2 weeks and the kids can go play on the swingset and trampoline without coming in covered in mosquito bites.

Just get some Bifen and nuke your yard.