Several Microdon sp. pupae in the first 2-3 inches of soil on top of mound nests of Formica sp.
See below for images of the larvae:
https://inaturalist.ca/observations/109172194
Adults reared to confirm ID
Pupae were kept in a container buried under 1 inch of moist (not soaking wet) soil at around 20-25 degrees Celsius. Adults emerged after 14 days under these conditions.