This species of wasp is a bit of an uncertainty. It is clearly associated with deadwood, where it provides for its larva as can be seen in the video below (which took some patience to collate).
Unfortunately, the quality is very poor, mostly on account of these wasps being so small and very fast, never staying still whilst out in the open. We have managed to obtain some half decent stills from this footage which make us feel this is likely a species from the Crossocerus genus.
On a couple of occassions you can see a quick flash of green. This isn’t the wasp itself, but rather the prey it is bringing to the nest, ready for when the larva need to feed.
For such a tiny insect it certainly managed to create a substantial nest by boring a hole into the rotting branch. It revisited the nest about every ten minutes over a period of several days…
Slightly disappointed not to get higher quality images of this impressive, if small, insect. Hopefully we will see more of them and their numerous closely related species in the years to come.