The Risks of Agriculture -- and of Caterpillars in Close Quarters
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 20th 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 20th 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.