From Chrysalis to Butterfly

One of the greatest aspects about having a kid is you get away with things that civilized adults in polite society can't. Of course, as a naturalist you can get away with them anyway as long as you're fine, or unaware, that you're labeled "eccentric," "adolescent," or whatever. While that actually flatters me more than anything (and why I love Monty Python, the Kids in the Hall, or any other comedy troupe that regularly sends up "businessmen"), it's still reassuring to know if pinned in a corner you can tie anything you do to your kid, " . . . it's a great learning experience for a pre-schooler!" Suddenly you're the parent of the year.

So, with continued great excitement, here is a decidedly non-birdy post following up on my my earlier excitement about our spicebush. This time I, er, Reina and I collected one of the spicebush caterpillars we found to watch the caterpillar-to-butterfly transition.

When we first found the caterpillars they were in their fourth instar.
Maybe next year we'll recognize an egg and watch the full process.

We didn't collect any until they reached the fifth instar stage. Not for any environmental reason, but mostly because we waffled about whether we should take one in captivity - where would we put it? By the purest of coincidences I walked by the "give-away" table in the staff lounge at the Lab and found a couple large vases for the taking - perfect caterpillar containers!

Unrolling a spicebush leaf revealed a beautiful fifth-instar caterpillar.

We had become experts in finding the rolled-up spicebush leaves that contained a caterpillar, though we were never sure what instar to expect. After enough experience you can probably guess correctly by the weight of the rolled-up leaf, startling your friends and perhaps taking in a few extra dollars for beer and chocolate milk money.

Once we found a leaf that contained the caterpillar we wanted we clipped the leaf and placed it in the thoroughly cleaned vase, added a few extra leaves and a branching twig from a recently-deposed Autumn Olive, and added a breathable top (my wife graciously gave up an old stocking for my, er our, observations), and placed it on the back porch.

Captive caterpillar, seemingly OK with its new surroundings.

I was never able to find any information about the timing of any transitions. We had no idea how long it had been a fifth instar so we couldn't predict how long until it turned to the prepupal orange-yellow stage. Once it became prepupal, how long until it formed a chrysalis? And from then, how long until butterfly emergence? Now we had a change to discover on our own.

I did learn that some pupae (chrysalids) are green and some are yellowish-brown, and that it was thought green ones will produce a butterfly this summer while brownish ones overwintered and emerged next spring. However, one site also debunked that hypothesis as some of their green ones overwintered and some brownish ones emerged the same year. Scientific observation and experimentation at its best: it seems to make sense that a green chrysalis would stand out during the winter months but blend nicely during the summer, while a brown one would mimic a dead leaf through the fall and winter. But when tested a seemingly logical hypothesis was not supported.

So, only knowing generally what to expect (if we did things right a butterfly was at the end of this process) we removed old leaves daily and added fresh ones, we watched often, and we even added a second fifth instar caterpillar a couple of days later. One Sunday morning, three days into the process we woke to find we were missing one of the "old" ones and a "new" caterpillar was in the vase.

Sunday morning it was greenish-yellow, by the time I took
images Sunday afternoon it had changed to the more
familiar pre-pupal orange-yellow coloring. But for how long?

Monday morning, one day after finding the prepupal larvae perched on top of a twig, we noticed it in a very awkward position, seemingly ready for chrysalis formation.

Leaning back on the underside of the twig, tail attached,
head suspended by a short thread. Soon a chrysalis?

Not wanting to miss the prepupal-to-pupal transition I set up the intervolemeter on my camera to shoot every minute, placed the tripod, and went off to work. When I got home nothing had changed, other than I have over a hundred images exactly like the one above. It stayed like that all day, but Tuesday morning, two days after turning prepupal and one day after "suspending" itself, we awoke to find a chrysalis.

The chrysalis suspended to the underside of the
twig by a central girdle of thread. I'm bummed we missed
the actual transformation, I'm dying to know how
it got from caterpillar to "suspended animation"!

I keep writing chrysalis and not cocoon: if you're unsure of the difference check here. Anyway, it started orange-yellow, like the prepupal larva, and slowly turned to a greenish, leaf-mimicking structure.


We hoped that indicated it would emerge this season, though that turns out to be dependent on a host of factors, such as temperature, photoperiod, and even information derived from the host plant. That's right, the caterpillar "knows," based on chemicals in the spicebush it was eating, on whether it's advantageous to emerge this season or wait until next spring.

If you looked carefully at the two pupa images you might notice they are actually close-ups of the two chrysalids side-by-side. I took those images after the second caterpillar pupated but hadn't yet turned color, giving a nice comparison.

The newer chrysalis is on the left, less than a day old.
The green one on the right is two days old.

I'm in complete awe of this process, especially one nagging question: how strong is that thread? How much can it take before it snaps?? I've been extremely careful every time we move anything, fearing it's going to slip loose. Reina, not so much: she's putting these guys through every natural bang-and-bump they'd experience in the wild.

As of today we're batting .500: one emerged 15 days after forming the chrysalis, the other is still pupating - 22 days and counting.

The adult after her first flight - I now call her female based on two
things: the bluish rather than blue-greenish scales on the upper
surface of the hindwing (to the best of what I can see and my
limited experience), and the fact Reina named her "Sara."

Any bets on that second one, will we see it this year, or perhaps next spring? Is it slower to emerge based on temperatures, photoperiod, or perhaps waiting until next year based on what the plant was telling it in the two-day difference between chrysalis formations? Perhaps something went wrong and it died during pupation.

My guess is we'll see something in the next week, it seems to becoming a lighter green along the sides and darker in the middle, perhaps indicating the black adult is there, soon to emerge. A fascinating process, whether you're four or, shall we say, "closing in on" forty.

• Interested in knowing more about Spicebush Swallowtails? Look at this Critter Catalog for all of the details!

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