Caterpillar Problems? I Got Caterpillar Solutions

Remember my black swallowtail caterpillars from last year? (And the year before that? And the year before that?) They came back! And then disappeared!

I had probably two dozen juvenile, first instar black swallowtail caterpillars on my year-two beast of a parsley plant in late June…until I didn’t. I had no new eggs or adult butterfly sighting for ages, either. Weirdly enough, a nearby friend mentioned to me that hers disappeared as well right at the same time. I have to assume that it was probably predation, as most birds and praying mantises and spiders and chalcid wasps and every other damn thing in my garden likes to crunch down my black swallowtail butterfly larvae like wriggly little potato chips. Not cool, guys. I didn’t squish or spray you, so stop eating my friends.

I also wonder if the heat and weird weather might have played a role–we had some scorching temperatures for a few days right before they went MIA. I was most afraid of some sort of local species-specific infection or disease affecting them–anyone who has raised black swallowtail or monarch caterpillars indoors without proper ventilation and humidity control has probably discovered that problem the hard way. (If you have theories about where they ran off to join the circus, pop ’em in the comments.)

I did find one very fat, very grumpy little fifth instar friend waggling his osmeterium at me indignantly when I brushed past his carrot leaf, so they’re not completely gone. I’m not sure if the presence of one indicates that he has siblings hiding in that dense foliage, but honestly it seems rude at this point to check after the  scolding I got from him.

Here are some of the most common problems I’ve seen from raising caterpillars, and my best guesses as to what went wrong. Contribute your own tips if you’ve got ’em!

My Black Swallowtail Caterpillars are Turning Black

This happened to me only once, and it was awful. I harvested about a dozen cats from my parsley plant and brought them inside to raise and observe in the safety of an old fish tank a friend had just given me. I left the lid on, thinking that I could use the light as some artificial sun for the benefit of the black swallowtail’s sense of timing and the potted parsley I put in with them. (Which they immediately stripped to stems in like, two days.) The first full day, I found that one cat had turned completely black and, I kid you not, it looked like it had liquefied. It was just hanging  limp off a stem, like the insides had turned to soup (prematurely, I mean. Innards turning to soup is a scheduled part of the caterpillar experience, but it’s meant to happen after they pupate.)

I removed the little guy, but by the next day, another six had gone the same way. At this point I didn’t dare relocate the few that were left back to the garden, since it seemed to be catching and spreading and I didn’t want to affect the wild population. They were all gone after two days, all turned black, all leaking, all a reminder of my many failures in butterfly husbandry.  Luckily, this particular failure was easy to fix.

The problem turned out to be ventilation. When I removed the lid to clean out the tank, it was noticeably humid inside and smelled strongly, even though there had been virtually no time for any frass or parsley debris to build up. I’m still not positive whether they got sick because of the humidity, or whether they came in sick and the humidity gave the disease the conditions it needed to take over, but removing the plastic lid and replacing it with a spare basement window screen across the top fixed the whole problem. I raised many more cats in there, and never had that problem again.

My Caterpillars are Going Limp and Turning to Mush

I’ve seen it a few times–the caterpillar goes inactive for a day or two, then goes completely limp, like a caterpillar smoothie inside of a caterpillar colored bag. (Sorry, it’s gross, but if you raise bugs indoors you’ve dealt with gross.)

I think I’ve dealt with this twice from two different causes–once I suspect that predatory wasps were the culprit, and another time I know for a fact that pesticides played a role.

I have heard (but have not eyewitnessed) that tiny chalcid wasps will parasitize black swallowtail caterpillar larva and chrysalises. Chrysalis? Chrysali?? Anyway, I’ve read that these teensy little wasps will lay their eggs inside of the chrysalis or the caterpillar itself. A parasitized chrysalis may turn dark (not to be confused with one that is dark because it was spun on a dark backdrop, or one that is dark because the butterfly is about to eclose.) Here’s someone else’s video of chalcid wasps emerging from an infected Monarch chrysalis if you want to see what it looks like, and how tiny these little guys really are. They emerge from a hole the size of a pinprick and they can get inside most enclosures.

Caterpillars Ate Store Bought Parsley, Promptly Died

You can probably guess what went wrong, here. What you wouldn’t know is that I washed the everloving bejeesus out of the parsley before I gave it to my hand raised caterpillars, and it still killed them within one feeding. (They had completely exhausted my home grown supply and it was either try to clean off the pesticides sufficiently or let them starve.) I have had success in the past with feeding store bought parsley when it was organic. It can be hard to find, though, not every grocery chain stocks organic fresh herbs. I might have had better luck at a Trader Joes or Wholefoods, but I can’t afford the kind of real estate that is close to a Trader Joes or Wholefoods, so I had to make due with the sad limp herb aisle at my Acme. I had already lost a few to store bought parsley, so when I tried it again I went about as thoroughly as I could conceivably have washed them without disintegrating the leaf entirely. I gave it several thorough rinses, swishing the bunch through a bowl of water and letting the faucet fun over them for a few minutes straight. (Not eco-conscious but I was trying to save some hungry little bugs because I’m a crazy person.)

I also applied more mechanical washing than I had the first time, thwacking the crap out of my stems and physically scrubbing them in my hands. The leaves were bruised to hell and back but I figured that if it didn’t work this time, I would know that there’s just no way to wash pesticide-treated herbs thoroughly enough to serve them to caterpillars and guarantee their safety. And apparently, there isn’t. (I think your own mileage may vary, here. I have served washed non-organic produce in the past and had them survive. Not being labeled organic doesn’t guarantee that pesticides were used or are still present, and it’s also possible that the problem is particular to whatever chemical was used by the particular grower, which there is no way of knowing. Considering the beating I gave the last batch I tried, I think it’s possible that whatever was used was not sitting on the surface of the leaves but was absorbed into the plant itself, which is a thing that can happen. Fun fact, this is why spinach and romaine can sometimes be contaminated with e coli that can’t be washed off–it’s in the water that went into the plant itself, so it’s inside the actual leaves.

Get Fat Forever Instead of Pupate Disease

I have no earthly clue why this sometimes happens, and I can think of nothing more descriptive to call it than that. Once or twice, I’ve had a cat that came in with several the same size, but kept right on eating after they had all pupated, getting humorously large before ultimately not surviving. I can’t fathom what would cause this, other than sheer force of will and a truly inspiring dedication to hedonism. Rock on, fat little dude, and live your best life. Apparently, every once in a great while, some caterpillars decide they don’t want to be butterflies, they want to be caterpillars, and do caterpillar things their entire life cycle. Who am I to judge their lifestyle choices, really? I basically just lay around and blog and snack all day, too. It’s awesome.

 Getting Eaten By a Cardinal Right-in-Freaking-Front-of-Me

Again: rude. I leave you birdfood and keep my cats safely indoors, there is no need for this disrespect.

Jury is out on the best way to protect garden caterpillars from birds. Some say not to put out birdfood so you have fewer birds. Some say to put out birdfood so you have fewer hungry birds. I think there’s merit to both–I don’t think either providing seed or not will either save or doom your caterpillars. For one thing, adults in the spring will catch a ton of bugs no matter what you do, because it’s not for them, it’s for their chicks. Laying birds and growing chicks need the extra nutrients and protein that bugs provide over seed. But summer birds are totally happy to chow down on seed that doesn’t go anywhere rather than chase bugs that do. So, if you are more committed to seeing butterflies than birds, I’d say maybe leave off the seed in the spring while they’re nesting, to maybe encourage a few more to hunt elsewhere, but go nuts in the summer content in the knowledge that they’ll probably go for the easier meal. I provide seed year round, myself. (And by year-round, assume I mean ‘when I remember to buy it and put it out.’)

How Do I Help Caterpillars Survive?

So what has all this experience raising caterpillars taught me? I have learned over the years to take a more laissez-faire approach. At the end of the day, birds are gonna bird. Wasps are gonna wasp. Caterpillars are gonna raze my plants to the ground and do their own thing, whether I help them along or not. I’m legitimately not sure whether my mistakes have killed more caterpillars than I’ve saved–you never know what their chances would have been in the wild. I think my presence in my town has contributed rather than detracted from the total butterfly population, but honestly that probably has more to do with my commitment to growing host and nectar plants and never using pesticides. They seem to get along fine both with and without me, either because or despite of my amateur butterfly raising skills. Honestly, things got easier once I started thinking about this as a fun hobby for me and not a necessity for them. They don’t need me to survive. I just create conditions that are more favorable to them, and in return I get to witness the neat things they do. They couldn’t give a crap either way.

I like to raise just a few caterpillars these days in a well ventilated fish tank on my porch and watch them do their thing, and let the rest fend for themselves in the relative safety of the garden I provide them. Whenever an adult black swallowtail visits my zinnias or sunflowers, I wave, and wonder whether it grew up on my porch, or hidden in my carrot foliage where I never noticed it, or across town on a Queen Anne’s lace flower growing out of a crack in the sidewalk. It’s part of the fun.

I used to make myself a lot crazier trying to save every caterpillar I could. I don’t regret the process, because I got to learn a lot and observe a lot of cool things and increase my own understanding of these insects and their lives. Whenever we’re dealing with wild fauna, the question is always ‘how much do we interfere’? Like I said about birds–do I encourage or discourage their presence in my garden? The biggest mistake I think we can make as gardeners and stewards is to think that we can or should control every variable for what happens outside. Remember that a lot of the problems I’ve experienced were things I caused myself by removing the caterpillars from the habitat the mother butterfly left them in when she peaced out. That doesn’t mean I think raising caterpillars inside is bad or dumb–I obviously still do it. I’ve just come to think of it as more for my benefit than theirs, and proceed accordingly. Would it be possible to raise caterpillars in a completely ideal environment? Maybe. Maybe we could create an enclosure that’s protected from birds but accessible to laying females, that’s got enough ventilation to prevent disease but doesn’t give access to tiny wasps, where they get the right amount of sun and temperature to follow their natural cycles without ever being frozen or scorched, and where I can provide enough foliage to sustain every egg that is laid (without accidentally stepping on a caterpillar when I trade out spent plants. That sound will forever after haunt me in my dreams.)

Maybe all that can be done! But I’ve never done it. I just do the best I can. Ultimately, I could try to control for wasps or birds, but the wasps and birds are supposed to be there. Chalcid wasps are supposed to attack some butterfly chrysalis. Baby birds are supposed to be given some caterpillars. Trying to control one variable always screws up another. Any pesticide you apply, I don’t care if its organic or vegan or homemade or “friendly to good bugs”–there’s no such thing as good bugs or bad bugs. There are bugs that happen to be  less convenient or more convenient to what we are trying to do in our yards, but that doesn’t mean they themselves aren’t supposed to exist or should be introduced where they don’t.

I’ll give you an example. Last year I bought a praying mantis egg case from a vendor at the local Philadelphia Flower Show. They’ve been marketed as a great “natural” pest control. I had a great time watching them hatch, and I felt so excited and privileged to catch a glimpse of a single full grown adult in my garden last year. This year, I’ve seen seven juveniles so far. During the most recent sighting, I found one in my herb box hidden under a basil leaf, a few feet away from my conspicuously empty parsley plants. It was chowing down on some unidentifiable bug it had caught at a truly impressive speed. Is that where all of my caterpillars went? I have no way of knowing. But if it is, I also have no way of putting that particular cat back into that particular bag, now that I’ve introduced them into my yard and they’ve created a stable breeding population. Am I going to try to capture or kill every mantid I see in my garden from now on to try to fix my mistake? No. Would I try again in the future to introduce another predatory insect control species that didn’t turn up on its own? Also no. Am I going to bring in something that eats mantids to balance things back out? HELL no! Come on folks, you’ve seen time travel movies, you know how it goes when you try to over-correct your mistakes. I’ll just know better for next time.

I hope this has been helpful. I’m gonna go poke my fat friend in my carrots because I think they’re funny when they get mad.