Thread-waisted Wasp
Ammophila ?
Observed at a muddy bank of the Sosiani River, Eldoret, Kenya, Dec. 2015.
This wasp is similar to Ammophila in Arizona yet looks as though it is gathering mud. Many sphecid wasps build their nests from mud, but Ammophila instead normally builds a gallery into sandy/loose soil. Perhaps it is just seeking water or salts or else will use some of the moisture and or mud to seal its gallery entrance. The galleries would be provisioned with caterpillars upon which the wasp young (larvae) will feed.