Why do most insects have a larvae stage, and what was the first?

I find it weird that flies, butterflies, moths, bees, hornets, beetles, ants, wasps, dragonflies, mosquitoes, and fireflies all have a larvae stage where they're just slow sacks of fat with a mouth. It seems so ridiculous to me that this trait is so prominent multiple species, so I'm wondering what was the... show more I find it weird that flies, butterflies, moths, bees, hornets, beetles, ants, wasps, dragonflies, mosquitoes, and fireflies all have a larvae stage where they're just slow sacks of fat with a mouth. It seems so ridiculous to me that this trait is so prominent multiple species, so I'm wondering what was the common ancestor that first started developing the metamorphosis trait, and why did it become so successful?
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