Magna- just seems more about magnetism, which is usually electric, though it can be a portmanteau of Magnanimous, which does work.
If I may make a small comment on this... Magna is a Latin adjective meaning "great". Magnus-a-um. Magna Carta. Great Charter. I don't think anyone using it in the name here is implying that CaP 4 has some magnetic element about it... If they were, I'd think they'd use magne- rather than magna to get that point across.
Also, regarding the use of "moth" in the name, I really don't think we need to be so anatomically correct when it comes to naming. It seems that people on here like to adhere to approximately the "normal" patterns of the games, but if you realize, there are a lot of instances in the Pokémon series where the Pokémon's name and its appearance don't exactly line up nicely. Think of Psyduck and Golduck. Psyduck is not a Psychic-type (despite learning a couple of Psychic-type moves) and Golduck isn't exactly gold either. Also look at Mothim. Four wings. Volcarona. Volcano + corona. Volcano is used here merely as an allusion to the Pokémon's Fire typing rather than its appearance (there's no sign of a volcano on its body. Neither can it learn Eruption, a word closely associated with volcanoes.) Similarily, the word "moth" in the names can merely be used as an allusion to the Bug typing. And I do think it resembles a moth-like insect.
Regarding its size, we can't really make an assumption here. KoA never gave a scale for his art submission so we don't know whether CaP 4 will be big or not. It's kind of a minor detail, and at this point I'm kind of nitpicking, but I don't think names that imply a large body structure should be disregarded just because bug is synonimous with small in size, and vice-versa. In fact, by choosing a name that implies a certain size to its body we can even get a general feel for those small details like height and weight that are usually decided towards the end, though that would be a poll jump in a way. In any case, that 600 BST certainly doesn't give
me the image of a Butterfree-sized Pokémon.
Alright, so maybe it wasn't a small comment after all...