My 2nd hugel (when it was 1-2 years old) attracted the attention of Yellowjackets
It was unpleasant to garden amongst those tiny beasts! My knee was swollen for weeks after the stung. I used the overturned glass bowl method; and they were successfully 'dispatched' without poisoning my garden.
While they were being starved under the bowl, I ordered coconut coir. When it was safe to dig in my hugel again, I mixed a coir slurry in a 40 gallon bucket (coir, fish emulsion, and a hose) and I filled in their void/nesting area.
Now, I cover or wash in coir, compost or dirt for my new hugels and if I see any subsidence during the season.