Venonat and Butterfree.

This is all fan fiction, none of this has been confirmed by game freak.

Have you ever noticed how similar venonat and butterfree are like? It almost looks as if venonat should evolve straight into butterfree, with their large compound-eyes effect and matching mouths and almost the same antennae. As well as this they also have matching feet and hand shapes.

Its the same with Caterpie, Metapod and Venomoth, they all have a similar kind of head ornament, and both Venomoth and Caterpie share the effect shield dust. They also have similar matching eyes and lower body grooves. If we look at an old sprite of venomoth, this is believed to be in Pokémon Green, you can see the yellow spots, which resemble caterpies yellow rings a lot.