I’m lucky to have landlords who alert me to the presence of interesting wildlife where I live, such as a large, mostly brown caterpillar my landlady found down by one of the lower ponds early in June. I thought it was probably the larva of a eastern tiger swallowtail butterfly, judging by the large eyespots on its back, which gives it a snakelike look to scare predators, and a yellow collar behind its head.
Eastern tigers lay a single egg at a time under the leaves of host plants, which include spicebush, tuliptree and several other trees and shrubs. When the cat hatches out, it looks like bird excrement, so not a big attraction for predators. As the cat grows, it morphs into four more instars (larval stages), eventually becoming mostly bright green. This makes it better camouflaged on the leaf as it eats its way toward pupation, where its exterior hardens, while inside the cat transforms into an adult.
But the cat my landlady found, while showing some dull green, was mostly brown, so I wanted to confirm the species. Before doing some research, I tried to place the cat on leaves of several of the eastern-tiger host plants so I could photograph it, but it kept trying to crawl off them, heading toward the ground. My landlady had also mentioned that she’d found the cat in grass, not on a host plant of the eastern tiger.
Judging by its behavior, I thought the cat might be getting ready to pupate. At that point, an ETS cat, like other butterfly species, leaves its host plant (to avoid predators that have learned to look for cats there), moving to a branch of a shrub or tree. Anchoring itself to the site with a few silk threads, it takes on the shape and color of a twig as camouflage during this vulnerable stage.
I left the cat inside my bug jar — with a tuliptree leaf, in case I was wrong about its getting ready to pupate, and with a bare twig from an ailanthus tree, in case I was right — while I tried to confirm its identity. I found a great account online of raising eastern tigers by Tony Gomez, who normally raises monarchs. He’d included photos of these butterflies in each stage, from egg to adult, including a photo of a cat about to pupate. It was brown, with the same markings as the one in my bug jar, so I was sure I had an eastern tiger.
My cat started to pupate on the twig in the jar within a few hours, fully encased in a chrysalis by the following day. I moved the twig, with the chrysalis attached, to a Port-a-Bug — a portable mesh bug cage that can be collapsed down to the size and shape of small pita and stuck in a pocket during field trips. Following the advice of experts in raising caterpillars, I hung the cage inside but near a window that is almost always open but out of direct sunlight. That way, the pupa would be exposed to varying temperatures and humidity as it would if it were in the wild but would be protected from the hot sun and the deluges of rain that are becoming more common here in the summer. To keep it adequately hydrated, I misted the chrysalis and the cage a couple of times a week.
While many lepidoptera stick to a schedule of about two weeks in morphing from a chrysalis to an adult, the eastern tiger often goes beyond that. My cat started to pupate on June 8, with the pupa fully formed by the next day and the adult emerging July 7, so a total of 29 days in transition. (See: a sidebar with more about of the metamorphosis inside the pupa and a slideshow of the metamorphosis of the eastern tiger swallowtail.)
An adult butterfly that emerges at this point in the breeding year has a short life with one purpose — reproducing — after which it dies. When the butterfly emerges, it perches somewhere near its chrysalis while pumping blood into its wings, which had been flat and folded up tightly in the chrysalis. As the wings expand and dry out, the butterfly starts flapping them, getting them in shape for flight. I was really hoping to observe this part of the metamorphosis, but luck was not with me.
I usually checked the status of the pupa several times a day but had a busy schedule the first week in July. I came home one evening just before dark to find the butterfly had already emerged and unfolded its wings while I was gone. Females of this species can look similar to males, which are yellow and black with tiger stripes, but they can also take a dark form, resembling a spicebush swallowtail but without spots on the body. The butterfly that emerged was a dark-form female.
Butterflies are diurnal and, with night setting in, I waited until the following morning to set this one free. As soon as the sun was up enough to get the butterfly going, I put her on some foliage at the edge of the yard, hoping that none of the local birds who hunt there around that time would find her before she could take off. She soon fluttered over to another bush. Still busy, I had to return to the house, not checking on her for a couple of hours. When I did, I couldn’t find her.
July started where I live with an explosion in blooms of wild bergamot, purple coneflower, meadow phlox and other native wildflowers in the various gardens in the yard, attracting increasing numbers of pollinators. Among them are eastern tigers and, a few spicebush swallowtails (which arrived later than usual). Having not tagged my butterfly, I have no idea if any of the dark-form female eastern tigers I’m seeing are the one that pupated in my bedroom, but I like to think she survived and hung around, helping to produce the next generation of her species.
© 2019 Pam Owen
How a caterpillar turns into a butterfly
I’ve always wondered how the miraculous change of a caterpillar to an adult butterfly or moth occurs inside a chrysalis. In finally doing some research after hosting the pupating ETS in my home, I found the process reminded me of the form of personal travel popular in science fiction: teleporting. This is often described as basically going from one place to another through a process in which the human body is disassembled into its atoms, then reassembled in the original form at the destination (although in science fiction, this often goes horribly wrong).
Butterflies do something like this but remain in the same place while disassembling and reassembling into a different form —in a matter of weeks. A 2012 article in Scientific American — prosaically titled “How Does a Caterpillar Turn into a Butterfly?” — does a great job of describing the metamorphosis, summarized below.
In the pupal stage, when the caterpillar is inside a chrysalis, it basically digests itself, except for what is called its “imaginal discs.” The discs are “certain highly organized groups of cells” that were formed in the egg from which the caterpillar hatched. Before hatching, when a caterpillar is still developing inside its egg, it grows one of these discs for each of the adult body parts it will need as a mature butterfly or moth. “Once a caterpillar has disintegrated all of its tissues except for the imaginal discs, those discs use the protein-rich soup all around them to fuel the rapid cell division required to form the wings, antennae, legs, eyes, genitals and all the other features of an adult butterfly or moth.” Check out the article for more details on this amazing process.