I had a similar problem at a house I used to own, only not as bad. Apparently, they eat rotting vegetation etc. Therefore, remove all leaves and grass clipping etc thoroughly and the blighters should move on on starve to death. It seemed to work for me.

There is a nematode available from Peter Stevens (08)82784465 which will kill millipedes. It will not be available this year until about March/April I think. I'm waiting for a call from him to get my lot this year. I have a friend who used them at Delamere and he tells me they were most effective - in the second year. It takes that long to spread the nematode. In the third and subsequent years he tells me he has seen almost no millipedes after literally millions around the house.

I have battled millipedes for years in SE Michigan. Beginning end of June/early July, they march across my driveway and emerge from behind retaining walls, many determined to crawl up the south facing walls of my house over night, walls that just happen to contain my garage overhead doors, so that I can usher them in with the opening of the door. Millipedes are relentless, stink to high heaven especially when threatened and stain areas where they cluster; and they reproduce at an alarming rate. During the summer, I can vacuum up hundreds of millipedes every day, off of the walls and from their favorite nesting places near the house. Aside from the vacuuming to control the population growth as well as the nuisance, I treat walls and perimeter with bifenthrin 4 times during the spring/summer months. I'm less than thrilled with the bifenthrin approach, but you'd have to be a pretty strong person to ignore thousands of millipedes crawling along your outside walls and across hardscape, decks, patios, etc.

So, all this seems to have made a dent in the population, but I am very interested in the nematode approach. Anybody aware of where I might obtain millipede destroying nematodes in the US?