Summer seems like it is finally here and I have been enjoying the good weather outside as much as possible. It seems to me that there is an abundance of butterflies this year, particularly the large yellow and black Swallowtail butterflies. And earlier this spring, I noticed many Mourning Cloak butterflies around as well. It could be that I am simply paying more attention, so in the absence of hard data don’t consider this a trend. My life has led me to butterflies, which means I am seeing and appreciating more of them during the fleeing time they are here, that is all.Butterflies under go what is called complete metamorphism, in that they have four fully differentiated stages of their development: egg, larva, though in the case of butterflies and moths the larva is by definition called a caterpillar, pupa and adult. Each of these forms is markedly different from the others, and this difference is one of the reasons we find insects so remarkable. The adult female lays the egg, typically one of hundreds of eggs, on or near an appropriate host plant for the soon to hatch caterpillar. The host plant is important, because as soon as the egg hatches, the caterpillar begins to eat, and it is usually pretty picky about what it likes (like so many kids). The caterpillar’s job is to eat and grow, which they do quite well, though most of them get eaten themselves, either directly by birds and other small hungry animals, or worse, by internal parasites. Many many other insects including certain flies and wasps use caterpillars as mobile feeding stations for their young. Eggs are either deposited directly into the caterpillar, or laid on host plant material, where the very hungry caterpillar unsuspectingly ingests the parasite egg. Once inside the caterpillar, the parasite egg hatches and the larva develops inside the caterpillar. Recall that the job of an insect larva is to eat. One source I read remarked casually that the parasitizing larva carefully eats the caterpillar alive from the inside, saving the vital organs for last, to keep the host caterpillar alive longer. If the caterpillar doesn’t get eaten or parasitized, it will grow. We think of caterpillars as soft and squishy, but really they must follow the same rules as all other arthropods. Arthropods have exoskeletons, and must molt, or shed their old exoskelton for a new larger one when they grow. Caterpillars do the same, shedding their tough outer skin. Each time they do this, they get bigger, and may even change color or shape, each version of the caterpillar is called an instar, for example you might identify a caterpillar as “the third instar of the eastern Tiger Swallowtail”. During the last molt or shedding of caterpillar skin, what emerges is not another caterpillar, but the pupa. This stage of the life cycle is often referred to as a resting stage, but really it is anything but. It is true that the pupa (contained in a chrystalis in butterflies and which occurs in the cocoon in moths) is usually immobile, but inside the protective exterior, the entire body of the caterpillar breaks down and is rearranged into an adult. The adult body structures form from just a few cells, sort of like stem cells, called imaginal discs, that originate in the insect egg, and are carried dormant inside the caterpillar all along. Just like us. A part of who you are comes from your maternal grandmother’s health and well being, as one of the eggs that became you developed in the embryo that became your mother inside your grandmother’s womb. Other bits of you come from your father, who continuously generates new genetic material throughout his life. As humans we take those bits of DNA and we develop, we grow, we age, we come into our fully articulated being, and we wonder where this person we’ve become came from. Just like the butterfly, emerging after so much work and shape shifting, we have to remember, we were there all along.
References:
Many online references exist for butterflies, none better than Bug Guide http://bugguide.net/node/view/81
A link from the Bug Guide site, to a California lepidopterist: http://mamba.bio.uci.edu/~pjbryant/biodiv/lepidopt/GettingIntoButterflies.htm
Bug Guide Mourning Cloak page: http://bugguide.net/node/view/3188
Good stuff on insect metamorphism from Scientific American: http://www.scientificamerican.com/article/insect-metamorphosis-evolution/
And specifically butterflies and moths: http://www.scientificamerican.com/article/caterpillar-butterfly-metamorphosis-explainer/
