Were Butterfree and Venomoth swapped during development?

Were Venomoth and Butterfree really swapped during the development of Pokémon Red and Green? Although Venonat and Butterfree are undeniably quite visually similar, I’d argue no; that this is rather due to simple design convergence. Essentially every design in generation one shares traits with something else, and that is consistently much more prevalent with bug-types since real world invertebrates are incredibly difficult to make palatable.

Generation one's designs were heavily restricted by the fact that they needed to be on 56x56 sprites, so evidently many shorthands for certain features or body plans were developed; simple bodyplans are reused repeatedly, while many lines shareeyes, limbs, and mouths - https://twitter.com/poondonkus/status/1492291313743577090

Examples include (but are not limited to) the "bracelets" of Primeape and Magmar, the weird prominence of giant tongues, the plastic-looking snouts of mons like Arcanine and Slowpoke, and most notoriously, gen one's "angry eyes". Designs drawn with this in mind are very similar or basic, especially compared to those of the present day. Furthermore, a lot of the similarities cited aren't very similar at all, or aren't evidence of much at all. With that said, Butterfree has much more in common with Caterpie than Venomoth does.

If you try to compare the sprites of both Butterfree and Venonat, they certainly look quite similar until you look at the finer details - 

If you look at the generation one sprites you can clearly see the similarities in features that look the same, such as the "angry eyes" and so on; while features that are meant to be interpreted different from similarly-shaped features have minute differences - for example, fur. These mons both have compound eyes, but they're differently structured.

Early artwork and even the gen two sprites highlight another drastic difference in the designs - Butterfree was black, while Venonat has always been purple. There was simply a change at some point along the way.

Looking elsewhere in the games themselves, Venomoth's index number is very far removed from Caterpie. Caterpie's line is all right next to each other; by the time they were implemented they were a complete family - https://twitter.com/DrLavaYT/status/1221679726776840193

I'm gonna take some time to debunk some things surrounding the theory itself -

One thing often cited are names; specifically the Japanese name of Venomoth - Morphon. Morpho is a genus of butterfly, and may refer to metamorphosis. This is a fairly strong piece of evidence at first glance, until you look at other names in Generation One. Pidgey's family are named after either pigeons (English) or doves (Japan) when they resemble neither - pigeon may just be a catchall term for "common bird". Tauros is Japanese is called "Centaur", when it's clearly just a bull. The names of many mons are used to evoke a vibe or describe a feature; Venonat to Venomoth is a drastic change. a metamorphosis if you will.

 

There's a couple ideas as to why these two would have been swapped - some involve the anime (which wasn't even conceptualized while the games were in production, and came over a year after the release of the games), and others suggest simply that the two were switched to make more sense to children. I find that latter argument to be a bit dumb; moths and butterflies are confused all the time, and children aren't gonna care about things like that anyways (look at Remoraid to Octillery or Carvanha to Shapedo, who's lines are linked by secondary concepts).

Furthermore, Venomoth is cute and serviceable as an early game bug design.
Adorable, ain't it?

These theories that designs were swapped are all incredibly lacking in substance (look at the idea that Dragonite and Gyarados were swapped, for example). They rely almost entirely on visual similarities but ignore the bigger picture. In this instance, that bigger picture is very important - it is hard to make a bug palatable. Insects are rigid, sharp, weird, ugly, and alien (I mean that in the best way possible). Humans love bugs when they either can't see that stuff (butterflies, bees) or there are cute, mammalian features (poodle moths, weevils).

The simplest way to make a palatable insect that everybody would want to own and care for (and again, one that can fit in a 56x56 sprite) is to simplify it immensely and make it cute. Big, round eyes complement simple bodies and a low limb count. Get rid of mandibles for smiles and sharp edges for round shapes.

That's what Pokémon does best. Look at designs like Ribombee, Leavanny, or Frosmoth. These bugs are sweet and friendly, so they're round, fluffy, and happy. An angry, aggressive bug is sharp and thorny, sure, but still keeps those round shapes and simple bodyplans. Araquanid is a six-legged, round spider, Pinsir and Heracross are both round, and even Beedrill itself adheres to this.

They've only strayed from this formula relatively recently, and that's just to make "cool" looking mons, like Golisopod, which would not be possible to have in a gen 1 sprite.

Pokémon's designs rely on being marketable, and in the early days on being simple. Naturally, a lot of designs have aged poorly, or look increasingly similar. That does not mean that there was some mistake during production, just that there's been a change in the design process in recent years.

I again emphasize that the hard facts we currently have do not seem to line up with this theory. This does not mean it could not have happened, nor does it mean the designs are not strikingly similar, it just means that there’s nothing to support that idea, and in the absence of facts suggesting otherwise, I’m inclined to believe that the two are not related.

Visual similarities, as I've shown above, are not indicators or a relationship, or else Parasect and Kingler would be related while Graveler and Golem would not. Inconsistencies between evolutions are commonplace, while convergence with others is equally as common - Venonat and Butterfree just seem to be nauseating examples of the latter, while the differences between Venonat and Venomoth appear to be examples of the former, at least going off of the current evidence.