caterpillar
蛅 centers on a caterpillar, a specific insect larva. The meaning is narrow, referring to this particular creature.
蛅 combines 虫 (insect) with 占, which likely contributes a phonetic element. The exact historical development is uncertain, but the insect radical clearly indicates a bug-related meaning.
The insect radical 虫 on the left and 占 on the right can be imagined as a caterpillar occupying a leaf: the caterpillar takes over the leaf like an insect claiming its spot.
For ネン, picture a caterpillar munching on a leaf, making a soft 'nen' sound with each bite: nen -> ネン, as the caterpillar steadily eats.
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