[IUFRO RG 7.03 FORENT] Ants in mailboxes

Any idea what kind of ant would do this? "2 days ago I had ants moving eggs into my mailbox. They were also building a white gossamer like nest much like that of a moth. I thought this was really weird....never have seen this in my life.... Then I mentioned it to my friend and low and behold ants were doing the same in her mailbox some 2 miles away." Ann Camp