Growing locale.X files

I have a replicaset with MongoDB 2.0.2 on twot Debian Linux 6.0 servers. The ReplicaSet is working fine. But on one of the servers I relalized that there are a bunch of locale.x files. For example local.0, local.1 ... local.22. Each of them 2.1 GB. The actual database/collections are less than 1 GB. I am just wondering why there are all this files and taking more than 40 GB space ??
On a dedicated server with 800 GB this is not a big deal, but on a small VServer with 60GB HD this could be a huge problem!