By Brannen Basham
Relative to most animals, human development from baby to adult is a simple affair.
Although we all experience the spurts, shocks and awkward stages of progressing from a juvenile into a grownup, even as babies we look like our future selves. This is not true for a good number of other life forms on Earth.
Frogs and toads begin their lives as gilled water dwellers, and slowly develop lungs, legs and other tools as they age. Many fish also change forms as they grow, such as flounders who literally have their perspective on the world altered by age as their eyes eventually wander to the same side of their bodies.
These changes are precisely regulated by hormones, and animals that undergo this transformation usually look and act very differently in their young and adult forms. Scientists refer to this change as a metamorphosis.
Insects take metamorphosis to the next level – in fact, all insects undergo a metamorphosis during their lives. While the true inner workings of insect metamorphosis are still waiting to be revealed, scientists have recently made breakthroughs that help illuminate the evolution and wonder of this incredible survival strategy.
The types of metamorphosis that insects go through are widely varied, and scientists have incorporated them into three types. Some insects undergo very little change other than size as they grow from egg to adult.
The scuttling silverfish is a prime example. These insects are believed to be remnants of ancient populations that have survived since long before the dinosaurs. Scientists believe that as insects spread and diversified, they also developed more complex methods of metamorphosis.
The first of these types to emerge was incomplete metamorphosis, which is when an insect has three forms – egg, nymph and adult. In their juvenile nymph form, these insects still resemble their adult forms but lack certain features such as wings.
Grasshoppers are an example of this; young grasshoppers live alongside adults in the same areas and share the same food with each other. Most recently, a large number of insects have developed the ability to undergo a complete metamorphosis. These animals live their lives in four distinct stages; an egg, a worm-like larva, an immobile and protected pupa, and finally an adult.
Scientists believe that complete metamorphosis most likely began with a series of mutations and lucky events, however it has a distinct evolutionary advantage over the other two types. Because each stage of complete metamorphosis is so different than the next, most of the time the larval form lives and eats very differently than the adult form.
This means that there is less competition for food and shelter between juveniles and adults of the same species, allowing for greater numbers of both in the same area. Bees, flies, butterflies, beetles and moths are some of the many types of insects that undergo a complete metamorphosis during their lives.
Caterpillar and moth metamorphosis has been intensely studied for a long time, in part because their large size as larvae make them easy to observe. Once inside their protective chrysalis, it seems that caterpillars release an enzyme that dissolves their juvenile form into a nutrient-rich slurry. Specialized groups of cells are able to survive the meltdown and use the goo around them to develop into the final adult form.
It appears that their brain survives the ordeal as well to some degree – to test this, in a recent experiment lab technicians kindly shocked groups of caterpillars and conditioned them to avoid certain situations. As these harried caterpillars emerged as adults, most actually retained this information and avoided future shocks.
Additional studies will hopefully uncover more secrets about insect metamorphosis, providing insight on ways to help imperiled species while also fighting invasive pests.
Brannen Basham and his wife, Jill Jacobs, operate Spriggly’s Beescaping, a business dedicated to the preservation of pollinators. He can be reached at email@example.com.