Even if the physical features seem to confuse, it can still be ascertained whether a larva is a caterpillar or a grub by closely observing its characteristics.
Only caterpillars grow into butterflies. Grubs will always metamorphose into bugs.
Butterflies are beautiful, tender, harmless to plants, and pollination agents. Meanwhile, bugs are rugged-looking, rigid, mostly harmful to plants, and are mostly considered pests.
Butterflies, no matter how big are some of them, they are very weak. Big bugs, such as the beetles, are very strong.
The Almighty created the butterflies for specific purposes just as bugs are made for other purposes that other creatures are not able to accomplish.
It is beyond natural metamorphosis if a grub transforms into a butterfly, or a caterpillar transforms into a beetle.
Transformation is God's preoccupation. He transforms sinners into saints.
But transforming a grub into a butterfly to do certain tasks that only beetles [can] do? That would be beyond human comprehension -- but not impossible by God's wisdom.