Yesterday I managed to video a Cerceris rybyensis that had ejected four paralysed halictine bees from a burrow. I saw no other female, but I am intrigued by this behaviour. Is this likely to be an instance of one female usurping another from a burrow? I have surmised that the new occupant of the burrow removed all the previous prey items, in case the competing female has already layed eggs on the cache of prey. The new occupant only wants her progeny to survive.
The video is here: http://www.youtube.com/watch?v=vMNLu_lidZo You can see the four paralysed bees that have been ejected from the burrow and the wasp in the background. A Myrmosa atra also puts in an appearance.
It was also intriguing that the burrow had two entrances. The wasp entered through one hole and came out via another, then flew down to the first entry and re-entered. So there must have been interconnected burrows within the bank.