Spewpa is the first cocoon Pokémon that is retains the same height as its pre-evolution, Scatterbug.
Spewpa, along with its revolutionary relatives, are the only Bug-Type Pokémons introduced in Generation VI.
Spewpa is the first pupa/cocoon type Pokémon in the recurring theme of "caterpillar, pupa then butterfly/moth"(like Metapod and Silcoon)Pokémons that took the least number of levels to became its final form(Vivillon), having only needing 3 level-ups(level 9 to 12) instead of 4(level 6 to 10).
Spewpa is the first of the cocoon theme to be able to learn Protect instead of solely "Harden" if caught in the wild.
Despite having a similar theme, Spewpa may actually look more like a bagworm, a type of caterpillar which undergoes a non-sessile pupal stage. Simply put, Spewpa looks like a fully mobile pupa which still can proceed to its imago stage.
Spewpa is most likely derived from the word "spew" and "pupa". The "spew" references the "spewing" of insects, and "pupa" because it is in a shell-like form, as well as being evolved from Scatterbug and the pre-evolution of Vivillon.