The animals of the land, the fish in the sea – they all start out their existences as microscopic, cylindrical, comma-shaped forms curled into the fetal position – as embryos. They mature in a womb or an egg – where their rudimentary appendages swell and lengthen, and skin grows hard, or scaly, feathered, or furry. Their bodies gradually evolve into shapes recognizable as miniature crickets, or sharks, or ducks – whatever the embryos are destined to look like when they are born.
This progression of the stages of development was set long before the age of the dinosaurs. But early on, one group of the animals came to alter the established order. Members of that group emerged from their eggs prematurely, still at their embryonic stage – naked shapes with vestigial legs on one end of cylindrical bodies. In this soft form they crawled forth to invade the land, and to grow monstrous (compared to the usual size of an embryo).
These creatures put off the appearance of their final stages, and came instead to gain their adult weight while still as immature, walking embryos. After this alternative staging of the embryonic program runs its course, they finally pause to harden their skin, reveal their sexual differences, lengthen legs and wings, and become aware of the world around them.
These were the metamorphic insects – the butterflies and moths, wasps and ants, the flies, and the beetles. Their adult lives are sort – they spend most of their days as embryos. They have taken advantage of a division of labor between stages – with the first stage specializing in eating and growing, and the second stage optimized for reproduction and dispersal. Living this double life, with immatures and adults occupying separate spaces, their two forms do not compete with each other. They have prospered with that alternative strategy, and multiplied the planet’s biodiversity many-fold. Today they are still the prevalent group of animals by number and by mass in most greenland places.
* * *
The two stages of those advanced insect orders have evolved greatly since they first appeared back in the Permean Era. The free-living embryos have entered many ecological roles, and honed their competitive survival strategies. Some of them have become parasites. The larvae of the stinging forms have become parasites on their own adults, living in nests – never to see the light until fully mature. When they emerge in adult form, they immediately set to the task of supporting and protecting their own next generations.
The beetles have risen to become the most numerous of the insect species. Their soft-bodied larval forms have occupied hundreds of thousands of niches around the world. Some have become brightly colored and poisonous, others have gone aquatic. The cylindrical, comma-shaped, sluggish, pallid larvae of some of them mature for years, ensconced in the dark within the rotting wood of standing snags in the forest. They grow to a foot in length, and to weigh almost a pound – a far cry from the microscopic stature of most embryos. Other beetle larvae have evolved the other way, to occupy smaller and smaller spaces until they have by now become too small to see. Still others have become consumers of detritus, and others have become predators.
Some of those beetle predators have reverted back to predation upon their own kind. An example of this is the ladybird beetles. Their adults and larvae will prey upon the larvae and eggs of closely related species, including their own. This helps the first-born among them to survive when the rest of them have eradicated their usual plant lice prey.
* * *
In the constantly evolving habitat around them, the beetles have become the most successful of survivors. Competition between the species has driven one ladybird beetle to cultivate one of its own microbial pathogens as a defense against predation. A microsporidian parasite now serves this beetle as a biological weapon – a defense for its eggs and young against other ladybirds. This animal is the Harliquin Ladybug – so named for its propensity to change its spots. Members of this species can show black with red spots, or red with black spots, or orange with zero to twenty two spots – just to list the most common color-morphs.
The microsporidian parasite’s spores fill the blood of the Harliquin Ladybug. But its blood is also filled with harmonine and other antimicrobial substances manufactured by the beetle. The concentrations of these substances in these ladybugs are so high that the beetles live surrounded by a faint odor of harmonine. The antibiotics serve to keep their blood-borne parasites under control. But should the aphid-lion larvae of another species of ladybird attack and eat the eggs or smaller larvae of the Harlequin species, the attackers are liable to come down with a microsporidian infection and die.
* * *
The great biodiversity brought to the Earth by the rise of the walking-embryo class of insects is now in steep decline. The current mass extinction, driven by the invasion of our own species, is still climbing toward its peak rate of animals lost per year. The last time a single species of organism caused an extinction of this magnitude was 2.4 billion years ago. That was when a cyanobacteria developed the advantage of photosynthetic metabolism. As their numbers grew, these microbes poured a by-product of that metabolism, oxygen gas, into the sky. When the atmosphere could no longer absorb the excess, the oxygen level began to rise. To the other creatures of the day oxygen gas was toxic, and they were all poisoned to death.
As the numbers of humans grow, they are crowding out the other species on the planet in many ways, including by poisoning their air and water. Our species has also caused the extinction of other animals and plants by the import of invasive competitor species to lands they would not naturally inhabit. One such careless import has been the Harlequin Ladybug. It was imported to Europe and the New World from Asia to enhance the control of agricultural plant lice pests.
Other ladybug species in Asia are adapted to deal with the biological weapons carried by their local Harlequin Ladybugs. But elsewhere, the native ladybugs are not prepared to deal with the toxic invaders. The invasive Harlequins can attack eggs and crawling larvae of the native ladybugs and survive, while the reciprocal predation kills off the larvae and adults of the natives. As a consequence, the over-all diversity of ladybugs is crashing. The common Seven Spot Ladybug and other North American and European species are being replaced across their range by the Harlequin, which then itself rises further in numbers to become a pest in its own right.
In biodiversity terms, the world is becoming a simpler place. Areas dominated by humankind – and that includes most greenland areas – have fallen under the domination of the same small cohort of weedy, human-adapted species of plants and animals all over the Earth. The great variety of natural species is dying out as their diverse habitats disappear under the growth of the human influence. Only the most adaptable survive.
The metamorphic insects are among the most adaptable. Though they are declining in step with the current mass extinction, their populations are now augmented by those of their numbers that have come to persevere in the areas dominated by man. Moths and beetles evolve defenses against control strategies designed to keep them out of agricultural fields. Ants and mosquitoes move indoors, into cities and human dwellings. Those of the insects whose larval stages feed on weedy plants are increasing. The insects with the walking embryo stage in their development will continue their history of evolving survival strategies – in spite of the destruction of the world they were born to.