The Saga of a Soggy Caterpillar

How long can you hold your breath? The current human record for holding one's breath is 24 minutes and three seconds, by professional diver Aleix Segura Vendrell. Wow! I can't hold mine for much longer than a minute. But even Mr. Vendrell's effort pales in comparison to insects-- some insects actually can hold their breath (that is, not inhale) for days! According to this article in Annals of the Entomological Society of America, larvae of various Cicindela Tiger Beetles can survive being submerged in hypoxic (low oxygen) water for between 60 and 120 hours. Wow.

But the tiger beetles have evolved that ability to survive, since their larvae burrow into sand which is liable to flood for days. What about solely terrestrial insects? Like, say, butterflies and their larvae? Turns out even they can survive a bit of dousing, or at least one of my caterpillars this summer did.

First instar Black Swallowtails are barely larger than the type on a park brochure!

One day I came home and checked on a day-old Black Swallowtail caterpillar like the one shown above, only to find that it had slipped under the surface of the water reservoir instead of staying on its dill sprig. (Note to self: watch out with tiny caterpillars and tiny dill sprigs!) My heart nearly stopped. I had even watched this egg being laid by the butterfly right beside me as I weeded the garden, so I was especially attached to this particular caterpillar. I had no idea how long the caterpillar had been underwater-- it could have happened hours ago. But just in case, I fished out the little body. How on earth do you give CPR to a millimeters-long caterpillar? For that matter, I don't know if you even could  do CPR for caterpillars. Like other insects, they breathe through multiple openings, called spiracles, along their sides. Mouth-to-mouth wouldn't exactly work.

Out of desperation, I just blew gently on the soggy, limp little black caterpillar. And it started to move! As the line from Monty Python and the Holy Grail goes, "I'm not dead yet!" I transferred the caterpillar carefully to a fresh sprig of dill, and kept it under close observation for a few days.

Once it was clear my caterpillar was out of danger, I became curious. Could caterpillars hold their breath at will? How, and for how long? This question sent me down a rabbit hole of research. I haven't yet found information specific to caterpillars, but did find one intriguing paper from 2005: "Insects breathe discontinuously to avoid oxygen toxicity," by Stefan K. Hetz and Timothy J. Bradley (Nature 433, 516-519). The researchers suggested that unlike us continual-breathers, insects keep their spiracles closed most of the time, opening them briefly and infrequently to release carbon dioxide and inhale just enough oxygen. The original paper is behind a paywall, but it's summarized in this article at LiveScience. So my caterpillar didn't hold its breath, exactly, so much as just keep its spiracles closed and use the oxygen already in its system, while it was underwater. Pretty cool!

Over the next few weeks, the caterpillar munched down all the dill I could provide, and grew quite normally. Despite the underwater episode, it actually turned out to be one of my largest caterpillars ever. Now, I don't actually measure my caterpillars, either their length or their overall weight-- I take a fairly hands-off approach most of the time. But just eyeballing, it seemed larger  than the other caterpillars I had raised a few days before.

So fat and happy! And no longer soggy in the least.

It pupated not long after I took this photo, and then successfully eclosed yesterday: a healthy female. Even my husband remarked that the butterfly seemed larger than usual, corresponding with its large larval size. After a few minutes of warming up in the sunshine, off it fluttered. Hooray!

The freshly eclosed Black Swallowtail, ready to fly off into my yard.

So moral of this story is: don't give up, even if your caterpillar falls into the water. They're amazingly resilient. No wonder they and other insects are predicted to take over the world someday!

Recap-- I'm back!

Hi again all, it's been a long time since I had the time/energy to post. But I haven't been completely neglecting my nature explorations over the past several months. Here are a few photos and stories for you. Enjoy, and hopefully I'll get back on a regular posting track soon!

A not-very clear shot of the first ever Rose-breasted Grosbeak to visit my yard feeder, back in May. Yay! I was so excited I hauled my husband over to the window to show him. He's not as bird-crazy as I am but he politely admired the bird with me. Awww. :-)

We found this spotted turtle at Huntley Meadows, sunbathing on a moss-covered log in the woods rather far from the water. I snapped several photos of the less-than-impressed turtle, as I have only ever seen one spotted turtle before (and that was injured on the road, so hardly counts). Eventually the turtle got sick of the paparazzi, however, and scuttled off into the underbrush.

 I take a walk at lunchtime every day at Brookside Gardens, and much of the summer I watched hummingbird clearwing moths (exact species unidentified). One day in July, however, I discovered something completely new to me: that the moths actually mate while flying, and continue to fly around in tandem for quite a while! I knew dragonflies & damselflies did this, but had never realized any moths did. This was the best shot I managed to get of the mating pair-- look about a third of the way down from the center top of the image.  Pretty cool.

 Here's a clearwing moth a bit closer, since you can't make out much detail in the paired shot above. They're really fun to watch as they hover and zip around. I spent many of my lunch hours trying to get good photos of them.

 I continued raising several generations of Black Swallowtails at my house, allowing dill (their larval foodplant) to practically take over my vegetable garden. Here's a shot of a chrysalis mere hours before the butterfly ecloses. You can really see the spots and stripes on the wing through the newly transparent chrysalis shell.

 Here's the butterfly an hour or two after eclosure. Behind it you can see a more recent chrysalis that's not yet transparent (so not eclosing anytime soon) and a caterpillar that's about to pupate as well. I invested in cheesecloth butterfly cages this summer, which are much easier to use than the tupperware, paper towel, and rubber band set-up I used last summer.

 Getting ready to free a butterfly. I bring the cage outside, still zipped up, then when we're safely out of doors I open it and reach in to coax the butterfly onto my fingers. If my husband is home to share the experience with me, sometimes he photographs the occasion, like for these shots.

A closer view of the butterfly being released. This one is a female-- you can tell by the extensive blue on the hindwings. Male Black Swallowtails have more yellow there. 

Dill wasn't the only thing I grew in my garden, even if it sometimes seemed that way. I planted the zucchini on purpose, but the delicata squash and other winter squash in this picture were actually volunteers from the home-made compost I added to the soil. So was the tomato; I planted a few tomatoes on purpose but none of them did as well as the volunteers did. Go figure! The delicata squash was delicious, by the way, especially sliced and roasted with a bit of salt. I'm definitely growing some on purpose next year!

 Another photo from my lunchtime walks at Brookside Gardens. I like to take photos of interesting and/or beautiful sights and share them in the evenings with my husband. Sort of like show and tell, I guess! His grandmother is in a nursing home at the moment, and can't get outside very much let alone see anything beautiful from her window. So I also like to share my Brookside Gardens pictures and stories with her when we visit.

I'm not a very strict weeder in the garden, I tend to let a lot of plants remain that technically shouldn't be there. Violets, shown here, are very hard to eradicate once they've moved in. However, several fritillary butterflies' caterpillars eat violets, so I always keep way too many violets in the garden. I've done this for years with no evidence that it was working, but this summer I finally found the spiky little caterpillar of a Variegated Fritillary. Woo-hoo! My lackadaisical weeding has been vindicated.

 This last picture isn't exactly in the way of nature studies, but it's too funny not to share. Earlier this fall my cat, Caleb, developed some sores that he kept biting and scratching. So the vet decreed he needed to be in this e-collar for a few weeks. Boy, did Caleb hate it! He did manage to figure out how to eat, drink, sleep, and use the litterbox successfully (the fact that it was a floppy collar, not one of the hard plastic ones, helped). But he despised the experience and thoroughly resented us for putting him through it, as you can see above. Poor kitty!

So that's some of what I've been up to since my last post. I hope you enjoyed the trip through my memories! I'll try to post again soon.

Butterfly success!

The suspense is finally over. The first of last fall's black swallowtail chrysalids (see here and here for the beginning of this story) is now a gorgeous butterfly!

Interestingly, the first caterpillar to change into chysalis is now the first butterfly.

After the caterpillars became chrysalids last fall, I just couldn't bear abandoning them outside, even to the relative safety of my garden shed. So I kept them inside on my desk all winter, silent little companions.

Then in early April I moved the chrysalids outside onto my back porch. I hoped the still-cool nights and gradually warming days would trigger the metamorphosis. I wired the twigs to an old chair beneath a maple tree, where they'd get late afternoon sun and still be protected from heavy rain.

I worried something could harm the chrysalids, but this was the safest spot I could find.

I've been checking the chrysalids every couple days since then for any sign of change. I had just about given up when two nights ago, I noticed one chrysalis had suddenly turned dark. I'd read that a day before eclosure the chrysalis skin turns translucent and the adult wing colors show through. I was too tired that evening to really think about it, though, let alone get a photo. Indeed, by the next morning I had totally forgotten about it.

When I got home from work in the evening, I started my normal routine of puttering in the garden. Finally though I remembered to go check the chrysalids.  I ambled into the back yard, not really expecting anything. But what a surprise-- the dark chrysalis was now an empty husk, with a beautifully formed butterfly dangling beneath it! I pelted inside to grab my camera, then spent the next forty minutes or so taking a zillion pictures and marveling at the gorgeous insect.

The butterfly flexed its new wings, allowing me to see the dark markings of a female. Pink cigars, anybody?

Tiny barbed feet clung to the old shell of the chrysalis. I wonder how long she hung there before I got home?

It was neat to be so close I could see the texture of  the antennae and the wings.

Almost ready to go...

Just a few short seconds after the last photo, I watched the butterfly climb up to the top of her twig, pause for half a heartbeat, then spread her wings and waft gently away. I lost her in the sunshine, but presume she soared upward to scope out the neighborhood and find a flower full of nectar. I don't have a lot blooming in my garden yet (the flower bed is still under construction) but I know there are plenty of blossoms nearby. My vegetable garden is also full of vigorous dill plants that sprouted from last fall's seeds, so I hope she returns once she has found a mate. I'll be examining the dill closely all summer, hoping I can repeat the cycle!

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.

My Dill Dreams Come True

I went into the garden this morning, planning to have a mellow photography session with the basil flowers and whatever bees came to nectar.  But only a few pollinators came by, and I wasn't getting any decent shots.  Then I happened to glance at the leggy, almost-dead dill plants and discovered the one bug I most hoped my garden would host:

A Black Swallowtail caterpillar!

There was just the one-- believe me, I looked for others.  Apparently female Black Swallowtails only lay a couple eggs in any one place.  But I am so thrilled!

I'm torn between leaving it wild in my garden, and bringing it inside to try and hand-rear.  I've never had success rearing caterpillars; when I was little we used to catch caterpillars every summer, in hopes of raising butterflies.  But they would inevitably die within days, partly because my sister and I knew nothing about the care and feeding of caterpillars.  We'd stuff their jar with miscellaneous grass and leaves, poke a few token holes in the top, and set it on the kitchen counter.  So I don't want to kill my only Black Swallowtail.  But on the other hand, I don't want the garden predators to catch it either-- I know my garden is also home to praying mantids, hunting spiders, wrens and chickadees.

For now I've left the caterpillar exactly where I found it.  I feel totally vindicated for leaving the scraggly, flopped-over  dill plants in the garden this long.  I know they look kind of ugly, and have scattered seeds everywhere--next spring I'll be digging out seedlings from the entire garden if not the whole yard. But it was worth it to see the caterpillar! I love having wildlife make a home in my yard.

Eat all the dill you want, little one!

Update: I found another one! The second caterpillar was about twice as big as the first. It's a lot greener, and was living in the carrot patch. Double hooray!

The real reason I planted carrots this year.

I even messed with it a little, poking it to provoke an alarm response. It shoots out a pair of bright orange fleshy horns, called its osmeterium, which apparently also stink (although I didn't notice any smell except the sweet scent of the carrots).

Get away from me!

Then since I had two caterpillars in the garden, I got brave enough to bring the large one inside.  I arranged a cozy little cage for it, with ample carrot greens to eat, a dried dill stalk to pupate from (eventually), and paper towels in the bottom to catch waste.

Home sweet home...

At first the caterpillar was disturbed enough by all the commotion that it stayed frozen on the greenery. But after fifteen or so minutes it moved down the leaf and started eating again! I was so proud.  Now there are several big fat frass pellets on the paper towels. The caterpillar is wandering around quite a bit too.  I am a very happy caterpillar mom.

Today's location: my yard, Montgomery County, MD