The "casings" are pupae of a moth.

The stages in a moth's life cycle include the following:

1. Egg
2. Caterpillar (the active feeding stage)
3. Pupa (a non-feeding stage while the caterpillar transforms into the adult)
4. Adult moth.

It is very hard to identify the specific moth species when they are in the pupal stage.

If you're curious, you can verify the moth species by rearing the pupae into adults. To do so, put the pupae and some of the soil in a clear container with a porous lid, perhaps a piece of toweling held in place with a rubber band. This allows for good air flow. Keep the soil moist by spraying with water, but take care not to saturate the soil.

Put the container somewhere you'll see it daily, but not in direct sun. When the adult moths emerge, use an identification tool like iNaturalist or Seek to see what matches. You can also submit photos to Ask Extension or your county Master Gardener volunteer program for help with identification.