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!

Monarch Caterpillars at Last!

This summer has been a very sparse one for caterpillars in my yard so far. I’ve found not a single Black Swallowtail egg or caterpillar, nor seen any adult butterflies. As I mentioned in this post about my Promethea Moth, I had only one overwintering Black Swallowtail chrysalis this spring, which eclosed shortly after its cage had blown away during a storm. By the time I found the cage again, the trapped butterfly (and its companion Spicebush Swallowtail) had died for lack of food. Poor things.

I hoped that the wild population did better than my captives, but I haven’t seen any signs of that yet. I’m letting dill volunteers sprout all over my garden, though, just in case there are a few wild Black Swallowtails nearby.

That being said, though, my caterpillar hobby didn’t go bust this summer after all. Over the last few weeks, my yard’s milkweed patch was finally discovered by Monarch butterflies! I have both swamp milkweed (Asclepias incarnata) and common milkweed (Asclepias syriaca). My husband spotted a Monarch paying special attention to the swamp milkweed while I was at work one day. When I checked those plants, I found my first monarch egg… and two plump caterpillars! Clearly there had been monarchs visiting my yard before that day too.

One of the first big happy caterpillars

The egg hatched just a few days later. I actually didn’t find the caterpillar the day it hatched—I forgot to check the cage that night. The next day, though, I discovered the tiny hatchling had wandered off its milkweed leaf onto the side of the cage. I quickly coaxed it onto a scrap of a milkweed leaf, and pinned that onto a fresh sprig of milkweed.

So tiny: how much smaller the hatchling is compared to the pin shaft!

Although I nearly had a heart attack when I realized the hatchling had gone without food for an unknown time, not staying on the milkweed probably saved it from being eaten by its ravenous companions. The two older caterpillars were now eating everything in sight, so I decided to keep two separate cages: one for eggs and hatchlings, and one for third-instar and older caterpillars.

Eggs and babies on the right, late-instar caterpillars on the left.

Over the next several days, I kept finding more eggs and caterpillars each time I went out to the milkweed patch. At first they were all on swamp milkweed, but eventually I found eggs on common milkweed as well. It seemed like every time I looked outside there was another monarch ovipositing! Eventually I gave up on collecting all of the eggs, as I was running out of room. I figure I’ll let the eggs hatch in the wild and then bring in caterpillars as I find them, so by then. As of this writing I have 21 caterpillars from tiny hatchlings to fat fourth-instars,  four more hanging in J, and four chrysalids. Whew!

A wild "j" that I found at Brookside Gardens a few years ago

The first two Monarch chrysalids

This sudden population explosion is actually pretty typical in my area. The monarch numbers have been silently building through the summer, culminating in the fourth and final generation, the migrators. (I think these caterpillars are the last generation, anyway.)

So far, it seems that Monarch caterpillars develop much faster than Black Swallowtails, especially transitioning from last instar to pupa. The two first caterpillars went from spinning their silk button to hanging in “j” (equivalent to how Black Swallowtails hang in their safety belts) to a glistening green chrysalis in about 24 hours! I didn’t get a photo of either caterpillar in j because of that, the speed really caught me by surprise. Black Swallowtails, on the other hand, usually spent a day or two in prepupa after spinning their safety belt, before finally molting into chrysalis. I don’t know how long the Monarchs spend in chrysalis yet, but as soon as the first two eclose I’ll be able to update this post.

Butterfly Update-- Eggs and Eclosures!

My garden's first Black Swallowtail egg of 2017

As I mentioned several months ago, I had a LOT of Black Swallowtail caterpillars at the end of the summer. I think I ended up with 26 (!) chrysalises to babysit over the winter. Sadly, three of them eclosed too soon. The first one was when the sun's seasonal shift sent a beam of light into their cage and warmed one chrysalis up way too early: in January/February. I handfed the butterfly (sugar water, in a 4:1 water to sugar ratio) from a cottonball for several days, and eventually set it free during one of the weird early thaws we had this winter. I knew it was unlikely the butterfly would live very long, let alone find many flowers for food, but I wanted a more natural life for the butterfly than constant captivity. Since that butterfly eclosed during a snowstorm, we named it Snowflake.

Then while we were away from the house for about a week a second butterfly eclosed. Unfortunately since it never got any food it died before we returned. Sorry, little one.

The last early eclosure happened during the storm Stella, in mid March. It was a male but I couldn't resist naming the butterfly after a blizzard, so Stella he was. Again I fed him by hand. Something interesting about both of these butterflies: they didn't seem to recognize when I put them on the moistened puff that it was food. I had to gently unroll the proboscis with a straightened paper clip and place the tip on the surface of the cotton ball to get both of them to eat. But as soon as they tasted the sugar water they were happy to suck it up. The second butterfly we also set free a few weeks after eclosure. It was still pretty early but I know Stella survived for at least 24 hours because I saw him soar back through my yard the next afternoon.

A few weeks later, once temperatures at night were reliably in the 40s, I put the cage of remaining chrysalises outside to start their natural end of diapause. Last week several butterflies eclosed: three females. Then two males this weekend, and finally another female two days ago. Today while bringing my tomato and basil seedlings outside for some sunshine I spotted a female Black Swallowtail in my garden laying eggs in my carrot greens. I followed her around and managed to find two eggs. I'm pretty sure she laid more than that, but they're really hard to spot.

So the cycle begins again! I hope I get more eggs soon, I have plenty of carrots and dill sprouting in the garden.

The second egg this year. I'm so excited for little tiny caterpillars to hatch!

How to raise caterpillars from eggs to butterflies

So you want to raise caterpillars. Congratulations! Maybe you want to help support the Monarch butterfly migration, or you want to share a biological investigation with your children, or you think it looks like fun. Whatever your reasons, I'm happy to help.

For the purposes of this post, I'm not going to go into how to get butterflies into your yard, that's another post. I'll assume at this point that you have a caterpillar or eggs in hand.

Please don't buy caterpillars online-- they may be sickly and you are very likely to find caterpillars in your own yard or garden, or in that of someone you may know. Many gardeners, if you ask them, would be overjoyed for you to remove caterpillars from their plants!

A Black Swallowtail caterpillar about to devour carrot greens.

Finding and Feeding caterpillars
Different types of butterflies need different hostplants for their caterpillars to eat. In my area the most common kind of butterfly is the Cabbage White (Pieris rapae). They aren't native to the U.S., but I think they're fine for your first try. It's easy to find a plant they'll eat: anything in the cabbage family -- radishes are probably the easiest and quickest to grow, and they're happy in a flowerpot if you don't have an in-ground garden. If you spot a radish whose leaves look pretty chewed up, that's a good clue you might find Cabbage White caterpillars on it.

Other caterpillars that are popular to raise include Black Swallowtails, which eat anything in the carrot family; and Monarchs, which eat any species of milkweed. My posts about raising caterpillars are collected here. Always make sure to identify caterpillars you find so you can provide the right hostplant. When I was a little girl I tried to raise caterpillars every summer by feeding them grass, because I didn't know they wouldn't eat just any plant. Of course, they all died. But you can do better!

Releasing one of my successful Black Swallowtails a few years ago.

Caterpillar Cages 
You'll need a container of some sort to keep your caterpillars in, that's closed to keep them safe. A jar  is fine with a paper towel or pantyhose fastened over the top. Your caterpillars will poop (a lot!), so to make cleanup easier, line the container with a piece of paper towel or even a coffee filter. Newly-hatched caterpillars are tiny, and their poops are barely bigger than dust, but soon the larvae will grow and so will the size of their frass (the actual name for caterpillar droppings). Leaving frass in the bottom of the container provides a great medium for nasty bacteria to grow, not a good idea.

My first set-up, with floral vial and paper towel.

When you are ready to move up in commitment (or your caterpillars get too big for their first container), you could use an old fish tank, even one that's no longer watertight. You can also buy professional caterpillar cages made of mesh. I have several of these cages-- one purchased at the thrift store, and four of different sizes that I bought online. You can see one above, where I'm releasing a butterfly. The benefit of the professional cages is that they let plenty of air through. They're collapsible too, so you can easily store them in the off-season.

Some DIY instructions are available here; a good discussion of different ways to set up a cage is here. The latter link is to Raising Butterflies' web site; their store also has good and relatively affordable cages. I can't remember where I originally bought my cages, but they look like the ones on Raising Butterflies.

This very hungry caterpillar is about to devour my carrot greens!

Feeding caterpillars, part 2
When raising caterpillars, you need to provide pesticide-free food for it. Ideally you'll have grown the plants yourself, but I realize not everybody has the space or time to do so. You may get permission from your neighbors, or even be lucky enough to find a vacant lot with the right hostplant.

If you don't have enough hostplants and neither do folks you know, another way to find food is to ask people you DON'T know. Join the Facebook group Raising Butterflies and Moths for Conservation; you'll find lots of helpful information there as well as like-minded folks. A simple post asking folks who live near you for help finding caterpillar food may solve all of your problems, as the friendly members tell you where you can find safe plants or offer you some from their own yards. Don't buy plants at the grocery store, even if they're organic. Organic farmers may treat their crops with Bacillus thuringiensis (or Bt), a bacterium that's deadly to caterpillars but harmless to people.

You don't need to put an entire plant in your caterpillar cage, cuttings are fine. Keep them fresh by placing stems in a cup of water, and make sure you protect the top of the cup so caterpillars can't fall in and drown. I use floral vials I get from buying roses; these are available online or at craft shops.

I prop my floral vials in a small glass inside the cage to keep them from falling.

Pupating
Your caterpillar will go through several instars, or stages, and molt each time between instars. Some species look different in different instars, like the Black Swallowtails I raise.The final molt will be into chrysalis.

Early instars of Black Swallowtails, like this little guy, are black and white; later they get green stripes as well.

When your caterpillar is close to that last molt, it will start wandering around. This is when it's essential to have your cage securely closed. My Black Swallowtail caterpillars walk a really long way, it seems, although I've never measured it. They're looking for just the right spot to make their chrysalis. At this point you should add a few twigs to the cage leaning against the walls at roughly a 45 degree angle.  If you can find twigs that have a few branches, that will give your caterpillars plenty of choice.

This little guy nearly escaped when I took the cage lid off for photographs.

One sign that your caterpillar is almost ready will be a final poop-- this will be very liquidy, not the compact frass you're used to. The caterpillar needs to get rid of any waste before spending days or even months in the closed case of its chrysalis.

Waste voided, this caterpillar is nearly ready to pupate.

Next the caterpillar will attach itself to a twig or the wall of the cage. It will spin a small button of silk and attach its abdominal end (cremaster) to that. Monarchs will then hang down vertically, eventually curling into a "J" shape. Swallowtails will spin themselves a sort of safety belt to support their front end and hang parallel to the wall or twig.

You can see the white silk belt the caterpillar spun to hold itself to the twig.

It takes a few days before the caterpillar actually molts. If you watch it closely you may see it occasionally twitching, like someone dreaming. I'm not sure what's going on here, but perhaps it's separating inside from the old caterpillar skin. When they molt, the chrysalis shell has already formed underneath the skin.

Halfway through shedding its caterpillar skin, you can see the chrysalis already emerging.

Depending on the species and generation, you may have to wait a couple weeks to several months for the butterfly to emerge, or eclose, from the chrysalis. I'll talk about that another time, plus what to do if a chrysalis falls.

Have fun! Let me know how your caterpillars fare.