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FUN FACT: One of the earliest Pokemon guidebooks (in fact, so early it's the first time Sugimori had to draw the Pokemon properly) explicitly notes that Butterfree's family is related, but not the Venonat family. This is related to the fact that Venomoth was created way later than Venonat, going by the index numbers and early polls, at least. Granted, the guidebook does something similar with Majikarp and Gyarados, as a joke.