During static observations where one does not move, all movements in the vicinity become apparent. It is a good observation method in general to get an impression of activity in a location. This is also the case while I’m observing nest building wasps. Regularly wingless Gelis females can be seen roaming the ground. This female Gelis spurius  crossed the digger wasp hill as I was dug into position for a digging beewulf female.
References1 Nederlands Soortenregister