The miracle of metamorphosis
We were walking along a path one fine spring day and came upon a large cocoon or chrysalis. You may remember from public school biology that this is the pupa and contains the transformational stage of a moth or butterfly.
Our remarkable find would likely produce one of the equally remarkable moths, possibly a polyphemus or a luna moth. We made mental notes of its location and even took a picture of it. We would be back.
As a timely refresher, this quick read will review the four distinct phases of metamorphosis, their purposes in the grand scheme of survival of the species, and their opportunities and limitations, both chemical and physical.
With deference to the old chicken and egg conundrum, most people prefer to believe that the egg had to have come first. So be it, we’ll begin with the egg.
The successful hatching of the egg is the prerequisite to all the stages that follow. The egg shell of insects is soft and contains sufficient energy to fulfill its function. In certain situations, the gypsy moth for example, if the eggs are laid on a mobile vehicle, such as a camper, the eggs will be dispersed over the landscape further increasing the survivability of the species. There are several limitations. The energy contained within the egg is highly sought after by many other critters, especially birds. Other natural factors, such as inclement weather can damage the eggs, but fortunately, there are very few predators or bacteria that affect insect eggs. Egg mortality is not common.
The larva is the stage that will emerge from the egg. The larval stage usually takes the form of a caterpillar and may be fuzzy and hairy, or not. The primary purpose of the larva is to eat. The larva is a feeding machine. And, while initially it may only feed at night, as it reaches its full size it may be seen eating night and day. Defoliation of stands of trees can devastate huge swaths of the landscape. Such successful feeding frenzies will dramatically contribute to survival. Such successful feeding also produced a lot of energy, which like the egg, is highly sought after.
The successful completion of the larval stage brings us back to where we began this short story, our large cocoon. This is a resting stage. Here is where the miracle of metamorphosis truly take place, where an adult will emerge. Adults in no way resemble the larva that encased itself in the chrysalis. The adult stage probably has the greatest potential to affect the survival of the species through reproduction and dissemination.
Reproduction is totally dependent on the uniting of the males with the females. Anything less is a failure. The male and female rolls are totally different. When the male emerges he will be identified by his two slender antennae. These antenna produce the chemical attractants called pheromones. All females within the range of his species unique pheromone, will home in on it.
Do you suppose there might be a human version of these pheromones at the corner store?
Females are also identified by their distinctive antennae which appear quite furry of feathery. To use a modern technical term, these antennae are microscopic GPS units or geo-locators. They will say, this is the way to your tall, dark, and handsome. One would think, over the eons, that this chemical system would be failsafe. Not so. Just as in DNA and our genetic sequencing, genes are subject to mutations. Types of mutagens include radiation, chemicals, and infectious agents. Mutations may be spontaneous in nature. Ultraviolet light is a form of radiation that acts as a mutagen, an agent that causes mutations in DNA. Also physical factors such as deluges of rain and high winds can disperse the pheromones. Insect control entomologists have synthesized species specific pheromones which have successfully disrupted reproduction. It’s definitely not failsafe.
Dispersal of the population is most commonly achieved by local weather or climactic frontal systems which can lift huge numbers of insects into the night air currents and transport them great distances over the landscape. This is a great plus for survival. But, on the contrary, there are predators. Bat research folks have recently been active in our community. They have noted that bats can be significant predators of insects active at night.
In conclusion, assuming sufficient adults successfully reproduced, another batch of eggs will be laid, and the miracle of metamorphosis will begin again.
Kim Mann
Duncan