I’ve been on a killing spree lately. No rampant caterpillar can escape from my smash…or at least my smashing ire. I’m conducting this purge because I’m an environmentalist. Ecology has turned me into a cold-blooded killer.

The standard picture of an environmentalist is often the gentle, peaceful hippie type, someone who expresses tender loving care for all plants and animals on the planet. They are caricatured as supporting all life and opposing all death and violence. As such, killing is not even remotely imagined as a tool that is in the environmentalist’s repertoire; in fact, it may be thought of as the antithesis. But the ecological household of nature operates differently from idealized notions of harmonious environmentalism. As the poet Tennyson would say, nature is ‘red in tooth and claw’; death, as well as life, are integral parts of nature. It is an eat or be eaten type of world, and death is as necessary to nature as every organism’s metabolism. Nature continues on unceasingly because it rests in an appropriate balance between the processes of life and death, fecundity and consumption. But unfortunately, the balance of nature can readily be tipped to a point of drastic change; there exist certain species that can escape their native habitats and alter the balance of the ecosystems in which they land. These species are known as non-native invasive species. Environmentalists and ecologists alike are thus faced with the quandary of whether it is right—and to what extent it is—to kill in order to restore the balance to native ecosystems.

One of the cast of characters that appears on the most harmful invasive species list is the gypsy moth (Lymantria dispar dispar). This innocuous little caterpillar—and its flightless adult moth—seem relatively benign singularly, yet the monstrosity of their sheer numbers has been an extreme detriment to the northeastern United States. Native to Europe, the gypsy moth was intentionally brought to America less than 150 years ago in 1869. A man by the name of Étienne Léopold Trouvelot imported the non-native moths with the intent of interbreeding them with silk worms to develop a more resilient silkworm industry. Trouvelot’s experiment inevitably failed, and whether intentional or not, the moths were released from his residence just outside of Boston. Lacking any of their natural predators to keep their population in check, just twenty years later the first major outbreak of gypsy moths occurred in Massachusetts. Trees were defoliated, caterpillars covered everything, and frass (i.e. insect excrement) rained down on the town. Since then, the gypsy moths have started on their relentless march across the northeastern United States. Each year, the gypsy moths stake claim to new habitat, and with it they bring their trail of destruction. Entire sections of forest can be defoliated in an outbreak scenario, and the creatures can easily defoliate more than a million acres of hardwood forest in a given summer.

Spread of Gypsy Moths in the United States, 1900-2007 (compiled by US Forest Service)

In early May, the next generation of gypsy moth caterpillars hatch from their over-wintering egg cases and commence their feast. They emerge by the millions and coat everything en masse. The tiny black-haired little crawlers make their visual appearance when they are about an eighth of an inch long, appearing on every natural or human-made object outdoors. The tiny caterpillars spin an elongated strand of silk and their long spikey hairs allow them to get carried by the wind to new places. To the casual observer, it seems like the tiny creatures are flying around. A young gypsy moth hopes to land on a palatable tree so it can begin its banquet and increase in size; barring an ideal landing zone, the caterpillars have a relentless drive to crawl over any obstacle to find a food source. In late spring, the observer can tell once again when the caterpillars have returned and can thus take action before much damage is done to the ecosystem. When the caterpillars are small, they are easy to destroy. Squashing the pests seems inconsequential. Pressing down upon them with a thumb produces nothing but a small black smear. Each caterpillar dispatched is gone forever and its life and memory are no more.

In early May the small gypsy moth caterpillars emerge and coat everything in sight.

But as the creatures grow, they become harder and harder to kill both physically and psychologically. They have been feeding for weeks, turning native plant leaves into more gypsy moth biomass. The caterpillars have become larger, less fragile creatures. When they reach half an inch long, they are sizeable enough to squirt out a blob of dark-green or bright-yellow juice whenever they are squashed. At an inch long, they begin to display an adverse reaction to being squeezed; it takes increasing pressure before the caterpillar is popped and its life juices run down the leaves. As the caterpillars keep growing larger, their features become more distinguishable; they have become stronger and actively resist death now with all their might. Killing the destructive organisms is now more of a struggle, particularly a psychological battle for the executioner. The juice that gets on one’s hands sometimes runs a deep red, reminding the slayer that it once belonged to the realm of the living. The breached corpses of the caterpillars clench indefinitely to their leaves even in death, a chilling reminder of the life that once was. These things remind the exterminator that the organism dispatched just moments ago was a living, moving creature.

Older gypsy moth caterpillars in the act of defoliating an apple tree.

What right do I have in taking a fellow creature’s life? Especially if they cause little direct harm to me? Is the fate of the ecosystem dependent upon my action as a concerned ecologist? Or should the gypsy moths be left alone and nature allowed to run her course? As the gypsy moth caterpillars grow, they continue to become more and more of a nuisance, even reaching plague proportions. They feverishly eat leaves, turning the native oak trees into Swiss cheese. Infestations can defoliate entire trees and can even lead to tree death; entire sections of native hardwood forest can be denuded by these insects. In a quiet moment in the forests of New England, the very sound of destruction can be heard from the tree-tops. Close your eyes and listen—it is not a sprinkle of rain you are hearing, but the falling frass of the swarm. The oak trees, and other hardwoods, suffer at the mouths of these non-native herbivores. The other native creatures that depend on the forests for food and habitat are adversely affected too. The greed of the gypsy moth’s appetite knows no bounds. Is it thus justified to kill the caterpillars for the sake of the trees and the forest in general?

The damage done to an Oak tree, the gypsy moth caterpillar’s favorite forage.

Should we as humans intervene in the situation of invasive species, even if it means the prescribed death of millions of organisms? It is a struggle that we as environmentalists and modern humans must face. Our civilized world has created a narrative that removes us from the brutal truth of ecological relationships and our impact on the natural world. The metabolism of life is neatly tucked away into the folds of textbooks or of the grocery store. We do not see where our food comes from, and we avert our eyes to predation in nature. We do not fully respect the fact that in order for the balance of nature to remain intact, life indeed must be taken. Death has become so unpalatable to our modern culture. It is thus exceedingly difficult to compromise a human distaste for killing with a commitment to the facts of ecology. I am both an environmentalist and an ecologist, yet I too struggle with the necessity of death. Humans are compassionate and sympathetic beings. It is hard to watch a young or injured animal die. We like to root for the underdog to survive. But not every organism in an ecosystem ever survives; it is not even physically possible for every organism in an ecosystem to survive. The balance of nature rests on the facts of metabolism—of life and death. When humans are responsible for bringing the balance of nature to a tipping-point, shouldn’t we also be responsible for correcting our wrongs? Isn’t killing another organism justified in the name of the ecological integrity of the whole system?

I encountered a similar moral dilemma surrounding the eradication of an invasive species when I was in Australia—only this example was more extreme. Instead of simply squashing caterpillars, the most-wanted organism was the cane toad. These creatures were much more relatable than a small caterpillar, and the moral qualms surrounding their eradication were much harder for me personally. The cane toad, a vertebrate, is much more closely related to human kind. Its blood and organs are similar to mine, and I felt as if I had some kind of evolutionary connection to the toad that I didn’t share with a caterpillar. Cane toads are also much larger—reaching up to the size of a dinner plate, and their deaths would prove all the more gruesome because of it. Though I knew intellectually how disruptive the cane toads were to the ecology of Australia, I individually had quite a few reservations about personally killing a cane toad.

Cane toads (Rhinella marina) were introduced to Australia from the tropical Americas in 1935 as a biological control method to combat the cane beetle, which was threatening Australia’s sugar cane crop. In 1935, 102 toads were released in agricultural areas in Queensland. From then to now, cane toad numbers have increased to more than 200 million in Australia today. Adding insult to injury, the introduced cane toads did not even control the cane beetles they were intended to ingest. Instead, cane toads wreak havoc by gorging themselves on native Australian fauna, eating native creatures directly and leaving less food for other native species. Additionally, the cane toads are highly poisonous and use their poison glands as their primary defense mechanism. Native Australian fauna, unfamiliar with the toads, see the meaty morsels as an easy meal. The cane toads do little to resist being bitten, and instead wait for the poison excreted from their skin to kill the pursuing predator. Instead of an easy meal, the Australian wildlife is poisoned to death. As the cane toads continued to hop into uncharted territory in the Australian bush, more and more native wildlife became diminished because of it.

The massive (and massively destructive) cane toad.

Cane toads have become a much bemoaned villain in Australia, and the culture Down Under is unsympathetic to the toads. Aussies will use whatever means possible to exterminate a toad. Drivers use them as target practice in the road. Kids use them as cricket balls for sporting events. Humane ethicists advise either freezing or drowning the toads as the most humane method of dispatching the pests. I too, was taught by the Australians to combat the spread of the toads by any means possible. As a backpacker lacking any real resources for the job, I was told to use my most powerful weapon—namely, my boots. I was taught to bluntly kick around the cane toads until they stopped dead.

As an ecologist, I felt that I had to fulfill my duty to an already ravaged ecosystem. And the cane toads were not hard to find. I stayed in many places in Queensland and northern New South Wales where cane toads covered the ground like a plague. Knowing about their negative ecological impact, I was ready to do something about it. At one roadside campsite near a creek and some slickrock, I encountered an abundance of the bedeviled toads. I singled one out. I picked it up by its warty back. Having no predators and no defenses other than their poison, the cane toad made no effort to resist. It didn’t even seem perturbed by being picked up. Holding the toad in my hand, I prepared for what was about to come. I let go of the toad and drop kicked it. The toad went flying onto the slickrock. I made my way to the toad. Dazed, but alive, I found it again. I had already committed to the extermination of this particular toad; it would be cowardly to back out now. Thinking thusly, I repeated the entire process a few more times. With each drop kick I imparted, I knew I was doing damage to the toad. Yet after every kick the toad still groggily got itself back up. I could still tell that the toad was every bit as alive as I was. My efforts at eradicating it simply weren’t enough. The toad wouldn’t be dispatched easily. From the outside, my toad looked every bit a toad as it did before my encounter. But on the inside, I knew, I must have done some damage. I knew I needed to end the suffering promptly and just kill the toad quickly. But I just couldn’t bring myself to the point of squashing down on the toad with my boot against the rock. I was appalled at the thought of the blood and the gore of it all. So instead I did the cowardly thing. I left the toad where I found it, hoping that it would soon die of its injuries. It seemed probable that the toad would have died soon after, but I’ll never know for certain. At any rate, my actions would not have produced anything akin to a quick, painless death. And now, I had to live with being the cause of that death. Though my hatred of cane toads caused me to maim one of their own, it could not overcome my desire to not take a life; all my beliefs about ecological integrity could not manage to win over my sentiments and cause me to end the toad’s life once and for all.

It is still possible that the cane toad I kicked around lived on. If so, the toad lived but it was the ecosystem that suffered because of it. Each cane toad, each gypsy moth that continues to live on in a place outside its native ecosystem continues to tip the balance of ecological resiliency. One does not see the consequences of continued ignorance towards invasive species individually. But collectively, the oak trees will suffer because of it. The native Australian fauna will suffer because of it too. The ecosystem as a whole suffers because of it. And thus, when an organism is causing undue harm as an invasive species, is it right to let it continue on and undermine the integrity of the ecosystem? I think not.

Though killing is psychologically painful, it is often necessary and justified for the sake of ecology.

For More Information:

• Cane Toads: An Unnatural History

• And the best scene from the film…

• And the sequel…Cane Toads: The Conquest