Surprise Moth Survival

Happy National Moth Week, all. To celebrate, I thought I'd share my experience raising a Promethea Moth, and how it seemingly came back from the dead.

Last summer I tried my hand at raising some moth caterpillars in addition to my usual Black Swallowtail butterflies. I have several spicebushes (Lindera benzoin) in my yard, and there’s more in the park down the street. So when I found this cluster of stripey caterpillars on the underside of a spicebush leaf, I was very intrigued!

The young caterpillars feed together early in their development, when they're striped like this.

Later the caterpillars changed their appearance and behavior. Rather than stripes, they now had black and yellow knobs on them, and no longer clustered together. Apparently this is common for this species: my guidebook says that Promethea Moths are gregarious when young, then wander off solo as they get older.

They also eat a lot of spicebush in order to grow so big and fat!

Only one of the three caterpillars made it all the way to cocoon; I’m not sure why. In fact, I only had two butterfly chrysalids to overwinter as well, one Spicebush Swallowtail and one Black Swallowtail. To be honest, I can’t remember why, although since I did finish up my Masters degree last fall I might have been too busy to check the garden as often as I usually do! 

Anyway, fast forward to this spring. In April, when the nights here are generally above freezing (usually about 40) but the days are starting to warm up, I put any overwintering chrysalids outside (I described this HERE). I put all three of my pupae in a single cage and hung it on our front porch. I thought I had it well secured, but my set-up couldn’t withstand the insane winds that came with a week of storms in May. (Neither could our roof, but that’s another story.)

I didn’t realize the cage was gone right away, but toward the end of the week I suddenly noticed it was missing. It took us a few days of searching before we finally found it next door, in a deep puddle in our neighbor’s yard. The cage was nearly flattened as well. When I opened the cage to see if anything was salvageable, I found two soggy, lifeless butterflies. They must have eclosed shortly after the cage blew away, but of course were trapped inside with no way to get food. Poor things. The moth cocoon still seemed intact, even if it too was soaking wet. I put it in a clean, dry cage and set that in my office, hoping just maybe the pupa was still alive.

I kept checking the cage every few days, but there were no signs of life for almost two months. I had just about decided that the pupa must have drowned after all. But then while tidying my office, I accidentally bumped the cage. Suddenly a large, very agitated moth was flying around inside! I had given up too soon on my pupa, but luckily hadn’t gotten around to putting it outside for decomposers to pick over. For once, procrastination comes to the rescue!

Anyway, I shouted for Victor to grab the camera, and we went outside to free the moth. After a brief exploration of my leg, the moth decided to perch on an antique bike that hangs on our front porch. Although its camouflage wasn’t as effective here as it would have been on a tree branch, the moth stayed there peacefully for several hours through the heat of the day. It wasn’t until mid-afternoon that it took off, when I inadvertently disturbed it by whistling for one of our cats. (I wonder if whistling normally bothers moths? Interesting.)

"Hmm, not quite right for my first day out."

"Ahh... that's better."

Check out those fantastic antennae! Gorgeous.

I'm pretty sure my moth was a male. Males are dark brown, with markings along the edge of their wings, where females are reddish with markings on their entire wings, as shown & described here and here.

I last saw the moth flying up over my house, toward the canopy of an oak tree that grows in between our house & the next house. An oak tree is a much better place for a moth to spend the rest of the daylight, anyway. I hope it did well! Silkmoths like the Promethea don't live terribly long in adult form. In fact they don't even have mouthparts, since they don't eat anymore once metamorphosing! No wonder they are such little pigs as larvae. Should my moth find a mate, of course, the spicebushes are ready and waiting to feed plenty of caterpillars. I'll certainly update here if I get a second generation.

So even though I failed to overwinter butterflies this year, I succeeded with my very first moth attempt! Pretty cool. Hope you had a good National Moth Week too!

Caterpillars Continued: From Poop to Pupation

So to catch you up since my last entry, I did go outside and bring in the original Black Swallowtail caterpillar to raise by hand, the littler one. Good thing I did, too, a few days later we started about a week of straight rain thanks to tropical storm Lee. How do caterpillars survive this much moisture? Even if they could find shelter I’d still think mold or fungus would be a serious threat with all the humidity. Anyway, now I had two caterpillars in the Tupperware container on my desk. (My apologies for taking so long to post, too-- this all happened last weekend, not the one just finished.  The school semester has started, so this week I've been a bit busy.)

Big caterpillar's in the far right of the carrots, little one's hanging under a far left dill stem.

Initial Observations

Boy, do caterpillars poop a lot! I have to say, these caterpillars’ poop, or frass, is some of the nicest smelling I’ve found from any critter. It reminds me of a rich field or forest, all decomposing plant material and fertile soil.  As they moved around and ate they also bruised the dill and carrot greens, releasing those scents too.  My office has been wonderfully fragrant this week! 

I noticed that the little caterpillar didn’t move around much; the big one was more active, roaming from carrot frond to carrot frond and of course eating a ton. The little caterpillar must have eaten too, judging from the two different sizes of frass pellets, but since its head was smaller I guess I couldn’t see the behavior as well. The two caterpillars were distinct individuals with their own preferences.  The big caterpillar, whom you’ll remember I had found in the carrot patch, preferred to eat carrot fronds.  The little caterpillar, who had been on the scraggly dill plants, occasionally tasted the carrots but would always go back to dill and obviously much preferred it.  This kind of worried me since there isn’t a whole lot of juicy dill left in my garden, most of it is dry and yellowed stems. But I picked what flowerheads I could find, and luckily some of the seeds from earlier flowers have sprouted into tender seedlings as well. If I must, I can always buy some organic dill at the grocery store. I’d rather use my own garden produce exclusively though.

My late summer dill patch.

The Drama Begins

I’ve had so much fun watching the caterpillars.  But I didn’t anticipate how much suspense and excitement there could be in caring for these little invertebrates. Since I had placed their container on my desk, I could see them as I worked on the computer.  Early Sunday morning-- two days after I adopted it-- I noticed the big caterpillar was even more active than normal.  It wandered restlessly all over the container, up the carrot stems, across the underside of the paper towel that topped the container, and back down to wander through the foliage again. Occasionally it would explore the dried dill stalk I had intended for a pupation site, but seemed unimpressed by it.

Checking out the dill stalk, with the little caterpillar in the background.

When the afternoon rolled around and the caterpillar was still wandering, I wondered if the dill stalk didn’t suit its preferences.  So I fetched a maple twig from our back yard, one as different from the smooth, pale stalk as possible: rough, dark gray bark, with a fork at the end to provide a choice of different vertical angles even. I wanted to be a good host! Soon the caterpillar discovered the new twig, meandered along it a few times but continued its restless wandering.  It must have walked the caterpillar equivalent of a couple miles, relative to its own length. I am impressed!

I kept both twigs in for a while; later I removed the dill stalk.

But Wait, There’s More

Eventually I realized that the smaller caterpillar hadn’t moved for quite some time.  I hoped it might be getting ready to molt, since I’d read that a period of inactivity often precedes molting. So now I made sure to watch both caterpillars all afternoon. As the hours ticked by, though, the big one just kept hiking around while the little guy rested on a dill flower stem.

Is is something in the air? Both caterpillars get ready.

Finally, at 3:20 Sunday afternoon, the big caterpillar stopped near the top of the new twig, as you see above. It spent the next couple hours in the same spot, turning back and forth every few minutes. Occasionally it would also rear its head and thorax back, leaning out into midair and waving gently back and forth. I also noticed it fussing on the lowest spot of its chosen site, apparently creating a button of silk to anchor its rear end to the twig. (The way a Black Swallowtail makes its chrysalis is first to spin a bit of sticky silk that will hold its rear to the twig, then create a loop of silk-- sort of a safety belt-- that will support it at the thorax while it's busy transforming.  After that it molts into its new chrysalis skin.) While it was working, gentle waves of faint movement also rippled down the caterpillar’s body from time to time, like tiny muscle contractions.

Safety Belt
Two long hours later, the caterpillar seemed satisfied that its hindmost prolegs were anchored securely on the twig.  More lengthwise convulsing ensued for a while. At 5:45 the caterpillar started rearing again, leaning way back into midair and waggling back and forth there. This time though when it returned to the twig it reached way around to the upper side. After fussing there, it reared again, wiggled, and reached around the twig again, this time in the opposite direction. Then it repeated this pattern. It was spinning its safety belt! It worked on the silk loop until 6:25, when it finally stopped. I hope caterpillars aren’t camera-shy, because I took a lot of pictures. 

Spinning the safety belt.

Still working on the safety belt; meanwhile the little guy stays motionless.

Finally done with the safety belt, it's time to rest.

Over the next couple hours it was mostly calm, relaxing in the safety belt that suspended it from the twig, with occasional twitching and fidgeting. I also noted more lengthwise contractions, like it was straining. I assume these were all because it has to loosen its old skin-- from the inside! By 10:00 pm it had pretty much stopped all movement and was no longer physically gripping the twig.

Look Ma, no prolegs!

Do Caterpillars Dream?

Now it hung totally dependent on the safety belt and the silk button. Once in a while it still twitched almost as if it was dreaming, but pretty much it just rested.  I expected it would start molting any minute, but hours ticked past. I stayed up long as I could, but eventually I had to give in. Even though I worried the caterpillar would molt overnight and I’d miss it, I really needed some sleep.

Monday morning when I came downstairs, I was torn between hope that the caterpillar had successfully transformed and trepidation that I had missed seeing it happen. But I discovered pretty much nothing had happened overnight after all.  It was still in the same position. The only change was its skin looked a bit drier and slightly flaccid, and it had taken on a brownish tinge instead of the bright grass green it wore the night before. 

Turning a bit brownish...

The other caterpillar, however, seemed to have come out of its quiescence. I saw it take a few tiny steps upward, then it rubbed its head against the dill stem.  I thought the caterpillar was eating, and that the previous inactivity had been just ordinary torpor. That was it for another several hours though, so I figured the little caterpillar just really liked to sleep.

Surprise

Not a whole lot happened in the container for most of the day. The prepupating caterpillar gradually appeared drier and more flaccid, and both caterpillars periodically twitched a tiny bit, almost as if they were dreaming. I mostly focused on my schoolwork, glancing at the caterpillars occasionally in case anything should happen. I expected there wouldn’t be any excitement until chrysalis time, but then at 4:19 the smaller caterpillar came out of its torpor once again, stretching vertically up the dill stem where it was perched. What was this—was I right the first time in thinking my little caterpillar was about to molt?  I started paying closer attention to it, but the real action took a long time to start. Finally, almost forty minutes later, the actual molt started for the little guy.

The head pushes out first-- the black thing in front  is its old head shield.

First it reared back, wriggling its head back and forth. Then it pushed its head upward, straining, and a new, pale green head finally popped out. The old head covering fell down against the stem, like a discarded mask. The caterpillar proceeded to climb slowly up the stem, squirming and straining to get out of the old skin, and finally waggled its tiny rump to get the last bit clear.  It only took about three minutes total once the shedding started!

The plump caterpillar pulls itself out of the old, wrinkly skin.

All clear! The old face covering fell away too.

The Excitement Doesn’t Stop

Next the caterpillar rested for almost an hour-- to allow its delicate new skin to harden some, and let the pigments in its head develop. You can see in these early photos that it has a completely pale green head. The dark stripes slowly developed over the next forty minutes. Finally at 5:42 the newly molted caterpillar, now sporting bright green stripes rather than the whitish stripes of yesterday, turned around & headed back down toward its shed skin.  I was excited to see the caterpillar devour its old skin (a growing caterpillar can’t afford to abandon those nutrients), so I got ready to take more photos. Just then, however, I noticed the big caterpillar had finally started to split its skin! I took a couple hasty shots of the little caterpillar and switched focus to the big caterpillar. 

Does shed skin even taste good?

You can just barely see the skin splitting over the caterpillar's back.

I’m a Caterpillar Paparazzo

I was so excited this was finally happening. I took a photo every couple seconds so I could record the full sequence. The caterpillar sort of shrugged the skin off over its hump with only a little wiggling, but then needed a whole lot of writhing and thrashing about to get it the rest of the way off.  It was still attached to the twig at the button and its safety belt of course, but within those limits the caterpillar moved a LOT. Imagine trying to wriggle yourself out of a too-tight mummy sleeping bag without being able to use your arms or separate your legs! What an ordeal.

The chrysalis starts to push itself out with great effort.

You can still see the legs on the skin as it peels off the chrysalis.

Just five minutes later the skin had been shucked all the way down to where the caterpillar was still attached to the twig by that silk button.  The caterpillar (now a chrysalis) swung itself back and forth a couple times and finally flung the discarded skin off, letting it fall to the bottom of the container. I guess the old skin must have split around the button, since the caterpillar/chrysalis remained attached to the twig the whole time.

The chrysalis just has to kick the shed skin off now...

Success!

The fallen skin. The other caterpillar didn't seem interested-- maybe it's rude to eat someone else's skin.

Last Step: Camouflage

The chrysalis wriggled a couple more times and then was pretty much still. The fresh chrysalis skin was mostly light green, veined almost like a leaf. I noticed tiny twitches periodically, much like the dream-twitches I noticed earlier when the caterpillar was loosening inside the old skin. By the next morning the chrysalis dried into a crispy-looking pale brown with darker markings.  It also seemed to shrink a bit over the next few days, ending up a tiny shriveled-looking thing. It looks much like a dry, curled-up leaf, to hide its presence over the winter.  It is astonishingly small, especially when I compare it to the freshly molted “little” caterpillar who is quickly growing big and plump. How on earth can the whole caterpillar fit in there, let alone develop those large gorgeous wings? Amazing.

The chrysalis turns brown overnight.

What’s Next

Usually we have about another month of warm weather around here, but Black Swallowtails have to overwinter as pupa. So in order to reproduce successfully, not only do my caterpillars have to make it through pupation, they also have to eclose (emerge from the chrysalis as an adult butterfly) with enough time to find a mate, lay eggs and then have those eggs hatch and make their own way all the way to chrysalis before the bitter winter hits.  The alternative is to enter diapause, where their development stays completely suspended all the winter. They’ll resume metamorphosis in spring. 

The online discussions of rearing Black Swallowtails that I’ve read indicate that Black Swallowtails are very unpredictable, but I suspect I will be chrysalis-sitting at least one, if not both, individuals all winter.  Quite a project! The other butterfly folks imply it’s not too hard though. An unheated shed, like my garden tool shed, is perfect for the almost-butterflies, who’ll stay safely in diapause until the weather warms.  Still I’ll have to check on them regularly, especially if we get any warm spells midwinter, which is common around here. For the time being, I'm still watching the "little" caterpillar grow rapidly bigger and plumper.  As of this posting, it's at least as big as the "big" caterpillar was at chrysalis time, maybe a little bigger. 

Just In Case

But what will I do if my butterflies eclose in the middle of the winter? I suppose I’ll build a large cage in my office for them, with flowering plants to feed the adult butterflies, and even dill or carrot plants to give them a spot to lay eggs if chance should favor me with one male and one female. Who knew that two tiny caterpillars could require so much responsibility? I definitely don’t regret taking them in, however. I’m glad to give them a much better chance of becoming adults than if they’d had to fend for themselves.  Even if they’d survived this week’s rain, their chrysalis perches could have been destroyed during autumn yardwork. I always look for interesting cocoons on dead vegetation before I remove it, and frequently even leave dead plants in place through spring to provide habitat for winter critters, but my neighbors tend to clean out their gardens before frost hits. 

This entry's location: My yard, Montgomery County, MD.