Next time any of my BAUT friends have this issue with underground nests there is a trick of insect psychology you can use against them. If you just bury the entrance they will just dig themselves out in short order.
Originally Posted by cosmocrazy
To kill them all you need to do is put a transparent glass bowl over the nest entrance. They fly out of their hole so they don't think they are buried and won't make another exit, then they die of dehydration in about two to three days.
Hope this helps somebody.
Time wasted having fun is not time wasted - Lennon
(John, not the other one.)