Mellininae is a very small subfamily of

wasp A wasp is any insect of the narrow-waisted suborder Apocrita of the order Hymenoptera which is neither a bee nor an ant; this excludes the broad-waisted sawflies (Symphyta), which look somewhat like wasps, but are in a separate suborder. Th ...

s, comprising only 17 described species in two genera. Occasionally this group has been treated as a separate family (Mellinidae), but has been more typically considered a subfamily within the all-inclusive family

Sphecidae The Sphecidae are a cosmopolitan family of wasps of the suborder Apocrita that includes sand wasps, mud daubers, and other thread-waisted wasps. The name Sphecidae was formerly given to a much larger grouping of wasps. This was found to be p ...

References

Catalog of Sphecidae that includes Mellininae, at Cal Academy
Crabronidae Apocrita subfamilies {{apoidea-stub