Why Metamorphosis?

A friend sent me a thought provoking article titled How Did Insect Metamorphosis Evolve? from Scientific American.  When you consider that everything an organism does uses some of its precious energy, something like metamorphosis doesn't initially make sense.

Incomplete metamorphosis *

First, consider what is involved in metamorphosis.  Incomplete metamorphosis refers to the process that insects such as grasshoppers, stick insects and a number of other species go through to grow.  It begins as an egg with a nymph emerging, undergoing molts while resembling the parent, although lacking the final stages of adulthood such as sexual organs and in many cases, complete wings.

Complete Metamorphosis begins as an egg which produces the larva.  After multiple molts, the larva pupates and emerges as a completely different organism, both in appearance and function.  Think of the caterpillar pupating and the butterfly emerging.

Complete metamorphosis *

Complete metamorphosis requires a lot of energy.  Any time an animal or plant expends energy, such as a deer growing horns or honey locust producing long thorns we assume that it had some advantage to the organism.  

The article above discusses the theories of how metamorphosis evolved.  At the last, it answers my question of "why bother to change forms?" Why curl up in a dormant state, wrapping the body in silk and then transform into a totally different body, frequently with not only different structures but even changing food sources such as changing from a herbivore to a predator?  There must be some survival value.  As the article states, "Metamorphosis was so successful that, today, as many as 65 percent of all animal species on the planet are metamorphosing insects."

So what is the advantage to metamorphosis?  Here is the answer in their words:

"The primary advantage of complete metamorphosis is eliminating competition between the young and old. Larval insects and adult insects occupy very different ecological niches. Whereas caterpillars are busy gorging themselves on leaves, completely disinterested in reproduction, butterflies are flitting from flower to flower in search of nectar and mates. Because larvae and adults do not compete with one another for space or resources, more of each can coexist relative to species in which the young and old live in the same places and eat the same things. Ultimately, the impetus for many of life's astounding transformations also explains insect metamorphosis: survival."

 Unfortunately this doesn't answer my last question- why does the honey locust still have thorns?

Thanks to Kevin Firth
*  Drawings from MuseumVictoria.com