As children develop an awareness of the world, they often grapple with the question of whether or not nature is cruel. Maybe as adults we still have occasion to wonder. Plants and animals are meeting their survival needs, continually evolving as species in ways that ensure that survival. Claws, poisons, sharp teeth, thorns, and other defense mechanisms can seem cruel or savage, especially when considered in human terms. We can see that the wasp was just defending its home, but this is hard to explain to a child who has just been stung.
Humans are a part of nature. Is violence among humans acceptable then? Are we just doing what nature does? I don’t think so. Our higher developed conscience carries understandings that foster responsibilities toward other life on earth, be it our species or others. Also, we are circumnavigating evolution in many ways with our health care advances and our ability to better protect ourselves from natural disasters. We are setting ourselves apart from nature for better or worse. Sometimes we seem incredibly advanced when I think of how much society and culture have changed over the last 10,000 years. Then I think of all the war, poverty, and crime that still exist. We don’t seem so advanced when I consider all the human rights violations that occur daily across our planet. We can probably never fully consider the needs of other species if we continue to denigrate our own species.
This is a huge and heavy topic! Yet, every summer I think about this subject when I find a parasitized tobacco hornworm in my garden. My feelings when I see this small part of a food web in action do not make sense. Before I had chickens, I would toss any hornworms over the fence, hoping they’d make it on their own, but figuring they probably wouldn’t. At least the problem of them dying – of me killing them – wasn’t in my ‘backyard’ anymore. Sometimes though, this callous act of mine would bother me enough to let one or two live, munching away on my prize tomatoes, because I love the beautiful Carolina Sphinx moth they become when they metamorphose. Now I feed any hornworms I find to my chickens, relishing the omega-3 fatty acids that will end up in my eggs someday. Isn’t a quick death more humane than starving to death on the other side of the fence?
The tobacco hornworm, Manduca sexta, feeds on plants in the Solanaceae family. Every year an adult female moth finds my tomato plants and lays her small green eggs on the underside of the leaves. I marvel at the adaptations that allow a flying insect to find the exact host it needs for its eggs, especially when the species is host specific like the relationship between Monarchs and milkweeds. Anyway, these little caterpillars grow fast and eat voraciously. They are so well camouflaged that I usually don’t notice them until their frass gets big enough. Frass is another name for poop, scientists’ way of sounding professional. Yes, the caterpillar’s poop gives it away! There are caterpillars that actually fling their frass away from the leaf, presumably to make it more difficult for predators to find them. However, the hornworm species hasn’t ‘figured’ this out yet.
Any garden plant we want to harvest is part of a very small food chain. In the case of the tomato, its food chain consists of: sun to plant to me! The word to represent arrows which show the direction of the flow of energy. Now, I wouldn’t get that tomato if a bee or other nectar-seeking insect didn’t pollinate the flowers, but that is a separate food chain connected to the food chain illustrated above. Two, or more, food chains connected together denote a food web. It would have a second arrow going from plant to bee (I’ve left out the decomposing part of these chains for simplicity’s sake).
We know that pollination has to happen for any plant in which we eat the fruit: tomatoes, peppers, beans, peas, apples, etc. So our simple food chain is already not so simple. Enter the tobacco hornworm. The caterpillar is a member of a third food chain we could add to this web, and he and I are in competition for that tomato. It’s getting more complicated. Then, if you’re unlucky, another creature joins the scene, the creature that inspired the topic of this post. This creature just wants to insure the survival of its offspring. Now this is where it gets gruesome, at least to me.
There is a parasitic braconid wasp that lays it eggs inside the body of the tobacco hornworm. When the wasp larvae hatch, they feed on the juices of the caterpillar. By the time I find the tobacco hornworm with small white egg-like projections on its body, it is way too late. These white projections are not eggs; they are the cocoons of the wasp larvae, which migrated (bore their way to the outside of their host’s body) before beginning to pupate. When metamorphosis is complete, they will fly away as adult wasps.
One would think I’d be thrilled. I don’t have to kill these caterpillars myself, problem solved, tomatoes saved. But I’m not thrilled. I’m horrified. I’ve studied ecology. I know this is just nature’s way, but part of me thinks oh how cruel! Something strange happens every time I stumble on a parasitized caterpillar. Those same caterpillars that I usually curse and view as nasty voracious eaters. When I see those cocoons and know what happened, I actually feel sorry for it. I can’t really empathize, and I don’t want to know what it feels like to be eaten from the inside out while still alive, energy fading day by day, but I just feel sad seeing it languishing. I leave it alone. There is nothing I can do for it.
I’m not sure I can say plants and animals are cruel despite my horror at the thought of dissolving from the inside out. Humans, however, are known to be cruel to each other and to other species. I am guilty – stinkbugs in my house get squished or flushed or squished and flushed. How can we practice more compassion for other life forms? Plant more trees, let a snake slither away, slow down on the roads, help a turtle cross the street, and, remember from last week’s post, don’t litter! Next time you see a spider in the house you could consider a capture and release – something my daughter and I do. These are small simple steps, but I think they matter. And next year, I’ll plant a few more tomato plants and I won’t feed all the hornworms to my chickens.