This August I tried hand-raising Monarch caterpillars. So far I've released 3 and have about 4 to go. Some of them I obtained as tiny eggs, others as partially grown caterpillars. I harvest Common Milkweed (Asclepias syriaca) for the caterpillars from the roadside or nearby abandoned fields. Plants in the milkweed family are the primary host plant for Monarch larvae. The fluid in these plants is a white, sticky substance containing a toxin. The toxin is tolerated only by Monarch larvae and some other insects that have evolved to feed upon it. The Monarch larvae, and the ensuing butterflies, are permeated with the toxin, which makes them a foul-tasting, potentially sickening morsel. The distinctive coloration of the larvae and adults signals a warning to would-be predators.
After a couple weeks of nonstop eating and growing, during which they shed their exoskeletons several times, they secure their posteriors beneath an overhanging stem with a silky substance. Dropping their heads, they assume a position in the shape of the letter "J." Within 24 hours, the caterpillar convulses and the exoskeleton splits open and falls away a final time, revealing a chrysalis of green and yellow, still ridged with abdominal segments. Soon, these ridges smooth away, and and the chrysalis becomes a pendant of opalescent pale green, studded with tiny gold jewels. The black stem is called a cremaster. Using a microscope one can see that the topmost end of the cremaster is composed of many tiny protrusions topped with knobby hooks. They appear to attach to the strands of the silk in much the same fashion as the human invention of velcro. After about 10 days, the chrysalis membrane becomes transparent. The body and wings of the adult butterfly can be seen inside, appearing almost completely jet black, with the exception of the deep orange pattern of the wings. The swirling shapes remind me of an Art Nouveau design of tree limbs silhouetted against a blazing sunset. I have yet to catch the exact moment of emergence. I think they wait until I leave the room! When I return there is the fresh, rather droopy winged adult, clinging to the remnant of it's casing. Over the next couple of hours, the Monarch balances delicately on four legs, turning itself from side to side, flexing its wings, unfurling its proboscis and wavering its front legs. Monarchs belong to a class of butterflies known as brushfoots ( Nymphalidae). These butterflies do not walk upon their furry front legs, but hold them flexed and close to their thorax. As the internal fluids transfer to strengthen and rigidify the wings, the body slims. Once during this process, I witnessed a drop of deep red fluid fall to stain the table beneath. Finally the wings are laid open in full color and shape. They slowly open, close, open, close, then suddenly take a maiden flight. The Monarch remains rather sluggish and calm for a while, enough time for me to take it on my finger and release it in a field tall with goldenrod blossoms. The butterfly shown below is a female. The wing pattern of a female has thicker veins of black than a male and lacks small black dots on the hind wings. Entomologists believe that the black dots on a male are vestigal organs. Evolutionary precursors of the Monarch emitted pheremones to scent pouches to lure females for mating. This generation is the last of the summer. The late summer Monarch butterflies in the eastern U.S will participate in a mass migration of 1000's of miles to a special place in the mountains of Mexico. There they will overwinter together in clouds of fluttering wings, clinging to the trees. The people who live there hold a festival each year to celebrate the return of the Monarchs. Traditionally, the Monarchs are believed to be the spirits of the people's ancestors.
In the spring, those Monarchs who have survived the winter will mate and begin the northward journey, laying eggs, then dying. The generation from these eggs will hatch as caterpillars, metamorphose into adults, continue northward, again mating and laying eggs, then dying. By the third or fourth generation, the butterflies have reached their northern terminus and the summer is ending. They must return to Mexico, a place they have never seen, to begin the cycle anew or perish. How do they do it? No one knows.