The Risks of Agriculture

The Risks of Agriculture -- and of Caterpillars in Close Quarters

Factory farming caterpillars.

Should I try to become the Smithfield Foods of the hickory horned devil production industry? I think not.

Most of the remaining hickory horned devils have pupated by now and most of the remaining lunas have made cocoons (again, email me if you would like any – otherwise, I’ll return them to the wild) but, frankly, I had a lot of late losses. This brings up a problem that is near and dear to my heart  (and related to the title of my blog)– the ecological problems that happen with agriculture.

What does "agriculture" have to do with raising caterpillars? Well, think about it – what is agriculture? It’s picking some species (or a set of species) that originally came from nature and creating special conditions that allow those species to prosper, unencumbered by the normal ecological balances that control population size and rapid growth – predators, disease, resource limitations, competition, bad weather, etc. Though it seems counter-intuitive to people who don’t know a lot about biology, these natural “checks and balances” are actually good for most species in the long-term, as they keep populations within “sustainable” (a word you’ve probably heard before) limits and, through natural selection, force the population to maximize the “fitness” (ability to survive) of its members, as well as maintain a healthy, diverse gene pool to address future needs. (A number of my previous posts have addressed these issues, as you may have noticed.) As the song says, “you’ve got to be cruel to be kind.”

With agriculture  – in other words, with human tampering to short-circuit this environmental system in order to increase an organism’s population for our own selfish purposes – predictably comes problems because the long-evolved  environment and ecosystem doesn’t  in fact just disappear when we start fooling with their parts. These predictable problems are really familiar to human civilization: exhaustion of soil nutrients (probably the biggest thing limiting agriculture and human population growth until the invention of artificial nitrogen fixation in the early 20^th Century), land degradation, weather-caused crop damage (especially from drought, especially before modern irrigation projects, though this is still a big,  unsolvable problem) and pests, predators, disease. These last three are really the ecosystem striking back, as the big monocultures that agriculture creates invite the complex biology of the environment to, as they say in business, “institute corrective measures.”

Pests (a term usually applied to insects) are mainly a problem with plant crops.  Big monocultures – vast fields of corn, wheat, cotton, soybeans – invite huge population explosions of the bugs that happen to be evolved to eat those specific plants. We mainly solve this problem through using huge quantities of arthropod-specific poisons we call pesticides, which, of course, cause other problems and are really only short-term solutions, because insects evolve and adapt quickly to poisons (see my earlier post on insect evolution and food plants) and eventually will become immune to anything that is not prohibitively toxic.

A big cornfield -- a monoculture of corn. The corn borer moth
thinks it has died and gone to heaven. It's just Iowa.

Predators (this is really a false distinction, since insect pests are really just predators of plants) are generally those parts of the ecosystem that attack livestock or animal agriculture – wolves eating sheep and cattle, hawks eating the chickens, etc. Since the predators of the few animals we grow commercially are not all that common in nature, we generally have “solved” this problem by eliminating livestock predators from the environment. This may seems like a good solution, but it too causes big problems. The population explosion of white tailed deer (and mice squirrels and other rodents that aren’t quite as noticeable)  and Canada Geese (now plaguing suburbs throughout the east), is a direct result of wolf elimination. And there are further downstream effects from that – you have perhaps heard of  Lyme Disease? It’s all only going to get worse.

And, finally, agricultural diseases – the problem topic I’m most interested in.  We don’t think much about the microbial ecology out there (the complex interactions is the biosphere of millions of species of bacteria, viruses and fungi) because we can’t see it . Our knowledge of these organisms is very new--we, in fact, really didn’t fully understand what the causes of disease were until the development of biology in the 20^th Century.  But  whether we know that microbes are playing a big part in the ecosystem or not, they still profoundly affect things. In plant agriculture, you simply can’t grow certain crops in parts of the country where certain diseases range. Wine grapes, for example, are basically impossible to grow in much of the American south where a certain leafhopper ranges, carrying with it a bacterial disease lethal to European grapes; the introduction of chestnut blight, a fungal pathogen, to North America basically eliminated the American chestnut, a once dominant tree in the eastern forests. If you are a wheat grower, just a single incidence of wheat rust is a major catastrophe, because it eliminates wheat as a crop, if it ever gets established.

This is all because monoculture itself is basically a complete denial of the realities of microbial ecology. In the environment, pathogens (microbes that kill or severely damage multicellular life) are relatively rare because (1) if a microbe evolves that destroys its host, it thus eliminates its food source (at least in the populations where it is present) and cause its own elimintatio; (2) pathogenic microbe populations are controlled by competition/predation by other more benign (and more successful) microbes in the microbial environment and (3) they are balanced by anti-microbial adaptations (like your immune system) that multi-cellular life forms have evolved over time. Generally, successful microbial species are those that have evolved to come to an ecological balance (think of it as a truce, or a trade agreement) with the hosts they live on/in and with the other microbes that also share that environment.

Monocultures mean growing organisms in unnatural crowds.
Pigs and chickens in factory farms.

Monoculture, which makes radical changes in the ecology, changes all that, eliminating many of the checks and balances and cooperative agreements that have been negotiated by the evolutionary process. This change thus allows microbes that otherwise not be well adapted to survive to actually flourish, and it gives a huge, easily accessible food supply for them to spread through with terrifying speed (hence the apt metaphor you sometimes hear of diseases spreading “like wildfire”).  “Easily accessible” is actually one of the largest ecological weaknesses in human agriculture: We grow vast fields of corn, house thousands of pigs in giant barns; in nature, populations are spread out across landscapes, mixed in with other competing species – if a new, deadly pathogen emerges, it may kill off a local population but then die off and subside before it’s presence in the environment becomes massive and it is a threat to the existence of the entire species. In other words, there are natural barriers to the uncontrolled spread of most pathogens.  By re-arranging things to suit our needs and wishes, we have unwittingly eliminated most of those barriers.

 The struggle with disease and microbial ecology is really the biggest problem in animal agriculture, and, frankly, it’s not a winnable battle.  We are currently using some very serious (and seriously dangerous) tools to combat this problem. Read up on the widespread use of antibiotics in livestock farming and Google “antibiotic resistance” if you want to begin understanding the catastrophe this is leading to. We simply can’t eliminate the unnatural spread of pathogens in monocultures of animals without causing still larger problems.

Make no mistake about it, growing caterpillars in sleeves is exactly the kind of unsustainable monoculture practice I have been describing, and, like any unwitting farmer, I’ve been plagued by totally predictable problems. As I’ve described in earlier posts, my unnaturally large populations and limited natural supply of nutrients (in my case, the sweet gum tree leaves that I can reach without a 12-foot step ladder) has led to problems – stunted growth and the lunas chewing through their sleeves, allowing parasites to attack. Then, further, the weakened populations of caterpillars became more susceptible to bacterial diseases, which, because of unnatural crowding, spread rapidly through my stock. The end result is that I only have about a dozen live pupae of each moth, after starting with over 200 eggs. You may remember me talking here in an early post about the natural adaptation of giant silk moths to spread their egg laying over a large geographic area and many trees. The catastrophic spread of disease under crowded conditions is yet another reason why that is necessary for the species.

Of course, my agriculture here has been small scale, and I have still had a modest success – I’ve successfully taken more caterpillars through the larval stage than  would have likely survived in nature.  Think of me being like a small, subsistence farmer, who has many farming disasters but still manages to grow more food crops than he could ordinarily forage from nature.  It’s still a disaster, but the practice is less unsustainable than what happens when you try to ramp it up to a larger scale. If there really was a big market for hickory horned devils, it might lead someone like me to think about developing a factory farm for moths… At which point, a wise person might consider pursuing another profession.

Bugs & Moonshine

Regal moth caterpillars in sleeves in my front yard. In the close-up you can see them -- they are about an inch long now. I used nylon screen for my sheeting material because it's hot here in Charlotte and I didn't want them to cook, but normally any thin fabric will do.

When I was a teenager, I made a fair amount of money for a couple of summers farming some unusual produce. No, it wasn’t illegal, though it was ethically sketchy (more on that later).  Actually, drug dealing would have been more socially acceptable among my peer group at the time.

Who wants to go back to school and answer the question “what did you do all summer, man?” with “I raised caterpillars in my backyard. Thousands of caterpillars…” and then, as the line goes in “Alice’s Restaurant,” “they all moved away from me on the bench.”

I grew up in a fairly small, fairly idyllic college town in upstate New York, where a lot of college students decided to stay every summer, to fill up the local swimming holes and take all the temporary summer jobs. This meant that local kids were pretty much out of luck for summer employment, unless you had a parent who owned a small business that boomed in the summer. I didn’t, which meant I was generally without pocket money  and had to spend a significant number of hours painting our house, chopping fireplace wood, mowing lawns, etc., etc., FOR FREE, because may father wanted to be sure I “was occupied.” As we said then, it was a “major bummer.”

I didn’t have a real job but, as I have said in a previous post, I did have a significant hobby – insect collecting. As a huge bug-geek, I got some insect collector newsletters, and one of them had classifieds, where people sold collecting equipment and … specimens. Reading these ads carefully, I noticed that some of these advertisers sold live bugs – notably giant silk moth cocoons. Collectors liked hatching moths to get “perfect condition” moths for their collections.  This gave me an idea.

I had grown caterpillars from eggs before and I knew the basic mechanics – catch female moths,  force them to lay eggs in paper bags, then find a source for the food plants. In the past, I’d grown caterpillars in dry aquariums. It was a lot of work, because you had to go out every day or so and cut fresh branches and clean the terrariums regularly or you got mold, which was yucky and killed the caterpillars. I knew there was a better way (there are instructions in some of the field guides) to do this outdoors with live plants, called “sleeving.”

Sleeving is a method by which you can farm caterpillars on a large scale. It’s a basic technology that, I suspect, was invented to grow silk moth caterpillars for the silk trade. “Technology,” in this case means a fabric tube that you can slide over a branch and tie tight at both ends, enclosing the caterpillars and the leaves. The idea is to keep the caterpillars from escaping and to protect them from predators – especially birds and parasitic wasps, which kill them in droves in the wild. If you make the sleeve big enough, you may never have to handle the caterpillars at all until they pupate. A bed sheet, sewed together at the long edges, is ideal, because the tube is big enough to enclose a large branch which can feed maybe a hundred caterpillars through their larval lives. Bed sheets are thin enough to allow the tube to “breathe,” so moisture doesn’t collect inside the tube and the caterpillars stay dry and healthy.

June was the prime collecting season for most of the large, showy, “collectable” moths in my region, and I had some great places to hunt them, a couple of miles away in the countryside, where mercury lights on some industrial and commercial buildings happened to be near some big open spaces and natural flyways. I and a couple of friends would ride out every night it wasn’t raining and collect. The year I started “farming,” we caught multiple gravid (fertilized) of all the locally common species of giant silk moth – luna, polyphemus, cecropia, io and even one promethia moth (not a common insect in upstate NY). We also caught egg-laying females of about 10 species of sphinx moths – otherwise known as hawkmoths – large bodied, often beautifully colored moths with long, powerful narrow wings. I had the raw materials to stock about a dozen large sleeves, though I knew that I might need even more when the caterpillars got bigger. It’s a little hard to guess how much forage a hundred  (or so) large caterpillars will eat.

I paid about $10 to put an ad in the newsletter, listing the pupas/cocoons I would have available later in the summer and their prices (I guessed at what I could ask, charging more for rarer species, and factored in the cost of mailing and supplies). I really had no idea if anyone would buy any, but I assumed somebody would buy something. I assumed my customers were kids like me, and a couple of years earlier, I would have bought some.

My mother, fortunately, had a lot of old, worn bedsheets which she didn’t mind getting rid of (I had to buy a few cheap sheets at Woolworth’s)and one of my friends’ mothers had a sewing machine and was willing to sew the tubes (our parents were largely academics, and they were willing to encourage strange hobbies). I had many of the food plants in my backyard, and another friend had a small patch of woods out behind his house which had the rest. I simply tied  the sleeves on the trees, cut the eggs out of the paper bags, put them in, tied the sleeves closed and waited.

Meanwhile, the mail started coming. I got nearly a hundred orders. Some of my customers ordered a lot of pupas. Some were business addresses in NYC, which, I  realized later, were dealers selling specimens to collectors around the world. My sphinx moth pupas were particularly popular because few of the semi-professional “growers” (there were not many back then, but there were a couple) bothered trying to growing them. My father, seeing the money roll in, largely let me escape from painting the house.

There was a folk song that I liked to sing back then:

Get you a copper kettle, get you a copper coil
    Fill it with new made corn mash and never more you'll toil
   You'll just lay there by the juniper while the moon is bright
Watch them jugs a-filling in the pale moonlight.

It was like that: vaguely weird, vaguely criminal (was shipping insects around the country through the mail legal? my dad wanted to know), and somehow beautifully lazy. It was fun riding around in the midsummer night  on my bike like a bandits, collecting moths, building my stock. It was easy work tending the caterpillars – I just made the rounds every few days, checking the sleeves, letting the droppings fall out, making sure there were plenty of leaves still left. It took me no more than 4 hours a week, at least when the caterpillars were small. It left a lot of time for lying in the hammock with a book and going swimming with my buddies in the gorges.

But there were some anxieties, as there is with any entrepreneurial venture. After I first put the eggs in the sleeves, I didn’t check them for two weeks, knowing they would take a while to hatch. We had a lot of rain and I worried that they might be drowned by it. When I opened the first bag, I saw nothing, absolutely nothing at first, and I immediately thought “Oh, no – I’m going to have to send all that money back!” Then I noticed a fine powder of minute droppings at the bottom of the bag… I started gently flipping through the leaves – there were tiny black cecropia caterpillars everywhere.

All-in-all, most of the caterpillars I was raising were very easy to grow, and sometimes they grew surprisingly quickly.   I would open a bag where nothing had been visible beforeand there would be a whole herd of large, odd-looking caterpillars grouped together on the twigs, like an alien invasion. Some of them thrashed or clicked their mandibles (they don’t really bite) when I alarmed them. I discovered that many of the sphinx caterpillars actually had multiple color forms within the same brood. Some of them were startlingly lovely, at least to my bug-loving eyes. Here are photos showing a few of the species I raised:

And, of course, there were farming “issues.” Raising these large caterpillars in a high density environment is not natural, and sometimes a sleeve would catch a disease, which would wipe out most of the caterpillars in it.  (All farming is unnatural in this way, and human farmers have had to deal with diseases and pests since the beginning.) One sleeve got raided by a raccoon, which tore open the tube and ate all the caterpillars.  (This is the caterpillar farming equivalent of the “cow in the corn.”) Fortunately, most of the losses were among the giant silk moths, where I had lower demand and duplicate broods.

And there was no agriculture textbook or cooperative extension officer for me to go for answers to some of the rearing questions I had. I had to figure a lot of things out by guesswork. Cecropias make their cocoons in the branches where they feed (easy) but lunas (harder) usually make their cocoons on the ground in the dead leaves. I put the luna caterpillars, once they stopped feeding, in a big cardboard box with a bunch of freshly picked loose leaves. An even bigger problem were the sphinx caterpillars (hardest) – they normally go to the ground, dig a burrow and pupate inside it. How do I duplicate an environment for that? I tried putting loose dirt in a box, but they didn’t like it and wouldn’t dig (I guess the dirt was too loose). I finally solved the problem by putting a six-inch layer of damp sphagnum moss, mixed with a little bit of regular dirt, in the boxes – this made a soft soil they could tunnel through. (The moss made good packing material for shipping later.) I learned some things about insect biology in raising these insects. How do you efficiently mail pupas? Art mailing tubes worked, and could be cut to custom lengths to match the order.

A sphinx caterpillar that is about to pupate. It's easy to tell: fifth instar caterpillars suddenly change color slightly (note the brown back), stop eating and start wandering. 

One big thing I learned was that I needed to pay attention to the insects if I wanted to understand them.  As they got big, I got nervous about how I would know to remove caterpillars when it was time for them to cocoon/pupate – if  I pulled them out too soon, would they starve?  As it turned out, it was a no-brainer. Caterpillars about to pupate change color slightly and begin to wildly wander. Every day, I would find a few at the bottom of the bag, wandering around: they were ready to go into a box.

In the end, I was able to make almost all my orders (I still had a lot of cocoons from some species left, which I let go when they hatched the next spring – I more than replentished my wild source), and, after paying for all my supplies and mailing, I made around $500, which was real money back in the late 60s. It was more than anyone else I knew made that summer – at least legally. I didn’t brag to other kids though --most people just wouldn’t understand.

I farmed caterpillars the following summer as well, and was almost as successful. I had repeat customers, which meant that the pupas I shipped had survived mailing. When I was in college years later, I was still getting inquiry letters asking if I had “stock” to sell.

Thinking back on it, caterpillar farming was both the best and oddest “job “ I ever had.  I didn’t know it, but I was an entrepreneur, and a biotech entrepreneur to boot. It was a job that required imagination, vision, a little bit of craziness, and just plain luck. It was fun, a-watchin them sleeves a-fillin, in the pale moonlight.

Imagining the Moth

The female regal moth I caught on July 26 was dead by last night, having laid 135 eggs (which entomologists call “ova” – scientists like to have their own jargon) . I’ve cut them out of the cardboard container I kept her in and put them in the clean glass container you see above for careful monitoring. The standard egg laying container is a paper grocery bag, but I didn’t have one, so I made due with  a stationary box, which did the job. They are the largest lepidoptera (butterfly/moth) eggs I’ve ever seen and they are a beautiful translucent green, except for a few, which are now partially brown. Those are that way because the eggs are transparent and you can actually see the embryonic caterpillars developing inside – the brown is their heads—I’m guessing some will hatch tomorrow. I have saplings of their foodplants ready in pots – when they are really little I want to grow them inside the house where I can control the environment.

Before you feel too sad for the moth who died for this , I need to say don’t fret – she accomplished her primary mission in life: laying eggs. Giant silk moths only survive a few days as adults in the wild, living entirely off fats that they accumulated as caterpillars. They have no functioning mouthparts and they don’t eat.  They have only two missions – to mate, and to lay as many eggs as possible.

I”ll talk about their mating behavior another time (because it’s an important topic), but their egg laying is also interesting. Regal moths, like many of their close kin, often fly great distances, depositing an egg or two on one tree, then flying a quarter mile to lay another egg. There are a lot of possible explanations for how this behavior evolved.(I like to call these “explanations” “hypotheses” because no one actually knows how the pressures of nature encouraged the behavior’s development, and, frankly, it’s hard to imagine an experiment that would prove the “real” cause. Honestly, what follows is all unproven speculation – intelligent guesses. In science, the next job would be to find some clever way to test these ideas – to design an experiment and then collect solid information – “data..” However, nature – the world outside is a messy, complicated place and coming up with intelligent designs for such experiments is very, very difficult. For now, I’ll stick to the fun, imaginative part – the hypotheses.

 My personal best guess  for why regal moths have evolved to fly long distances and lay single eggs is that, since these eggs grow into very big caterpillars, it would be a bad idea for too many of them to be on one tree because they are likely to attract the attention of predators (such as birds) and once a predator has found one caterpillar, it is going to be primed to see another one nearby. So, this hypothesis says I saved the female moth the effort of flying all over the forest to lay her eggs, so she probably was able to get more laid before her fat-stored energy ran out (fat is really just a chemical battery, if you think about it). She had to lay them all together, which might be disastrous in nature where there are birds, but I’ve got her back – I’ll protect her caterpillars from predators. This makes me the good guy. Really.

However there is another “hypothesis” for why this moth has evolved single egg rather than mass laying behavior and this explanation perhaps means that I’m not being so clever in “farming” these caterpillars. Some of the regal moth’s near relatives, the oakworm moths (species in the genus Anisota), do tend to lay their eggs in big masses, and the caterpillars feed together in big troops, especially when they are young. (Herding together must serve some kind of protective function for these caterpillars, like it does for bison and schooling fish and ducks and starlings and the like, but I have no idea how that works – make your own hypothesis.) Oak moth caterpillars are considerably smaller than regal moth caterpillars at maturity and they grow up faster. Importantly, this means they have less time chance to catch a disease that could spread from caterpillar to caterpillar quickly, wiping out all a moth’s brood in one rapid epidemic.

       Young oakworm moth (A. osalari) caterpillars. National Park Service photo by Sally King.

This is a familiar problem to anyone who has ever tried to raise a lot of giant silk moth caterpillars  – you have to grow them in crowded conditions (you’re really “farming” them) and various diseases can appear and destroy your project. So perhaps another explanation (hypothesis) for why the regal moth lays single eggs is that this protects long-maturing caterpillars from spreading the diseases a few are likely to catch during a long period of infancy. This could be the explanation, or both explanations could be right or… something else entirely might be the cause. Nature is complicated and it’s hard to imagine all the problems that might come up in the life of a moth.

But it’s still fun to make guesses about the evolution of unusual characteristics in a species. One other feature of regal moth egg laying behavior that I also think is a bit strange is the fact that these moths produce only one generation a year, even here in the south where summers are long. This is actually not typical of most giant silk moths. Lunas, for example, have at least two generations a summer here in North Carolina, and researchers have noticed that they have three in Texas. The first lunas hatch and lay eggs in April here, but the regal moth waits until the end of July or August to hatch, mate and start laying eggs. Why?

We can reject the explanation that the moth has only enough time for one generation a year because it is so big that it takes a long time to grow. It does take a relatively long time to grow, but not really that much longer than a luna, which goes through the whole cycle twice. So let’s add another piece of evidence: its closest relatives (other species in the sub-family Ceratocampinae) also have only one generation (one “brood” as scientists say, or “univoltine” behavior) though many are much smaller moths. The authors of The Wild Silk Moths of North America  have suggested what I think is a convincing hypothesis for this: “In the United States and Canada the greatest number of species occur in the Southeast. Midsummer flight in warm, humid weather maybe an adaptation related to the tropical affinities of the group.” In other words, the authors note that relatives of these insects are a lot more common in the American tropics, so species like the regal moth may represent relatively recent invaders from tropical climates and they may still have hold-over physical adaptations from their not-too distant past, such as favoring the time of the year when North Carolina feels like Mexico or Honduras. In the tropics, the moths lay eggs in the rainy season, since that’s when the food plants are freshest. Perhaps these tropical moths have carried the home country behaviors here.

 This is another perhaps un-provable hypothesis regarding evolution, but I like it because it again makes you expand your imagination to consider yet another dimension that can affect things: history. Consider the fact that only a little over ten thousand years ago (a blink of an eye in biological history, really) most of North America was covered by the expansion of a thick ice sheet. (Ice might have been a mile thick where I live now.) When that happened, where did all trees, bugs and other animals go? They either died out or they moved south to where there was no ice (Florida would have been ice free, but much cooler than now.) Then, when the ice receded back to the north, old species returned and some new species invaded from the south. The regal moth and its relatives may have been just such invaders – they still carry the signs of their history in the way they live.

So, in order to come to grips with how a moth works you need to imagine all kinds of things – what it’s really like out there – and what it must have been like out there a long time ago. Who knows what the most important “causes” were? There were certainly many, all working together and the result of the biological evolution they caused is the moth we have now. To really know we await clever minds, brilliant experiments and … data.