Saturday, April 03, 2010
March of the Chenilles 2010
Beneath the Chinese elm tree canopy I noticed the caterpillar poo on the sidewalk just before the ides of March. I tried to see them, the mourning cloak (Nymphalis antiopa) larvae that must be up there feeding, but the distance, the bright sun, and my feeble eyes kept them hidden. No matter, even without the telltale droppings phenology would have caterpillars up there maturing this time of year.
The next day, March 13, the march was on. Caterpillars (and other insects with complete metamorphic life cycles) leave the munching grounds of their youth to pupate. It seems reasonable to imagine this migration could work to thwart predators that may already know where the caterpillars are. Anyway, the caterpillars were on the move, some of them crossing the street, a few were climbing back up the elm trunk from whence they came, but many of them found a convenient vertical surface like our house. A typical one would climb up a ways, stop, search around with its head, turn 90 degrees, climb a ways, turn again, etc, sometimes heading back down. Finally, by the next morning they had assumed the head-down J position of a caterpillar about to pupate after finding I guess the perfect spot. By afternoon of the third day, March 15, the pupae were on their ways to becoming butterflies.
I kept an eye on the pupae, and mid-morning April 3 noticed one of the butterflies had emerged. At 11:00 am, I photographed another pupa. You can see the stripes on the wing edges right through the chrysalis. Within an hour, this butterfly also emerged. So it took most of the pupae 19 days to complete the transformation to adults. One of them emerged the next day late in the afternoon, and remained hanging onto its former shell for the rest of the day. The following day was rainy, and the late-bloomer hung on all of that day too. By the next sunny morning it had flown off.
After a butterfly emerges, it will hang wings down as the wing veins expand as they fill with fluid and then harden. During this period the butterfly will expel some red liquid known as meconium, which is waste product from the metabolic change from caterpillar to butterfly. Here you can see some of that on my house beneath a hanging butterfly.