Melissa is a 7-year-old, entomologist. While the other children are throwing pots on the wheel, making clay figures or building bird houses, Melissa is puttering about in the Dianthus searching for slugs. She is culling the ground for beetle larva, or searching for aphids and lady bugs. She usually has a few slugs on her chest and an inchworm or caterpillar in hand. She has learned to identify metallic wood-boring beetle larva, cut worm larva (which usually turn into moths) and slug eggs.
Most of us remember from science class (if I may be so bold as to be a spokesperson for the human race) that Arthropods; insects, Crustaceans and Arachnids have exo (exteriors) skeletons.
And that humans and other mammals, birds, fish and things that go bump in the night have endo (inside) skeletons. Actually many things that go bump in the night have exoskeletons too.
Inside we contain a hard, erect sculpture of bone, wrapped neatly in tissues, muscles, flesh and fat. If, like arthropods we had soft insides and hard outsides, there would be no weight watchers or Jenny Craig. Liposuction and lap bands would never have been invented.
Arthropods are limited by their external skeleton. It’s like wearing a corset 24 hours a day. If they can’t control their appetites, they must take extreme measures; usually involving something dramatic like splitting their backs open or turning into liquid and reforming.
We of the soft outsides can grow and grow until we can’t leave the house.
We think of caterpillars as soft squishy things that transform into chrysalis (or pupae) and emerge as butterflies. But this is not really true. Caterpillars are arthropods too. They may appear soft and squishy, but even they are encased in a hard(ish) shell. If you don’t believe me just squash one!
When caterpillars emerge from eggs they are small, very, very small, about 1/8” ( 2-6 mm) long. Before they can become a chrysalis they must grow between 30-50 times their original size.
They eat and eat and eat and eat, like Orson Wells on a bender. But unlike Orson their flesh cannot expand indefinitely. Eventually their outside gets hard and tight. They’re not comfortable in their own skin.
They spit some silk from their lower lip (if caterpillars have lips) and attach it to a branch. They appear still, but inside they’re wriggling. About 24 hours later, they have managed to scrunch down inside their skin and their head pops off! Or so it seems, but actually it’s only the shell of their head. Caterpillars don’t like living in their heads, so out they crawl, to eat and eat some more.
First they eat their old skin, then they move onto milkweed (Asclepias). Milkweed is slightly toxic and gives them a nasty taste. A bird who snacks on a caterpillar will not try that snack again!
Before they are ready to begin the grand metamorphosis into butterflies monarchs caterpillars must molt five times. Each of these stages is called an instar.
Inside the chrysalis, the caterpillar has dissolved into goo and its body is reformed, becoming a butterfly. This process takes 10 – 14 days. The cooler it is, the longer it takes.
When the adult is ready to emerge, the chrysalis fades from green and gold to black and transparent, through the chrysalis you can see the pattern of wings.
The chrysalis splits open and the butterfly wriggles out. Out drips a blood-like substance. It is meconium, liquid waste mixed with extra pigment, yum.
Its delicate wings are crinkled and wet. The butterfly hangs upside-down and pumps blood into its wings, inflating them. It waits several hours for its wings to dry before flying.
Females begin laying eggs immediately after their first mating.
Adults that emerge in the summer live for two to five weeks.
But when the weather begins to turn cold, butterflies, like birds and retired folk go south.
The last generation of monarchs to hatch at summer’s end flies to central Mexico or California. (Depending on their milkweed accounts.)
This is the Methuselah generation– which can survive for 9 months— outliving the combined lifespan of their parents, grandparents, great-grandparents, and great-great-grandparents. It is this generation of butterflies that migrates from Canada and the United States to either Mexico (if they are east of the Rocky Mountains) or to the Southern California coast (if they are west of the Rocky Mountains.) This last generation of summer enters a non-reproductive phase known as diapause. This generation winters in the sun and generally does not reproduce until it leaves the winter site sometime in February or March.
No single individual makes the entire round trip. Female monarchs deposit eggs for the next generation during these migrations. The first generation may reach as far north as Texas and Oklahoma during the spring migration. It is the second, third and fourth generations that return to their northern locations in the United States and Canada in the spring.
Using a genetic GPS based in their antennae the monarchs are able to determine the angle of the sun and head due south. Thus they travel a journey that neither they, nor their parents, grand parents, great-grandparents or great-great-grandparents have ever made before.
Monarch butterflies are one of the few insects capable of making trans-Atlantic crossings and they don’t have to pay for any extra baggage.