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The struggle with invasive caterpillars

2021 07 03 caterpillars          By David Hawke -- This week’s column is about gypsy moths; more precisely it’s about the caterpillar stage of the gypsy moth’s life cycle.

In short, I don’t like them, not even one tiny bit. However, begrudgingly, I do admire them as they are survivors.

          I have no doubt that many readers have had to deal with these crawling nuisances for the past few weeks, either sweeping off patios or wrapping tree trunks in burlap. And you have all reached the same conclusion I have… it just does not seem to be making dent in their population.

          So, I guess it’s time to discuss this clash of natural events with the intersection of human nature. First, the natural events.

          These moths (now renamed Lymantria dispar dispar or LDD) were brought to North America about 150 years ago as part of a commercial venture to find an alternative to the cotton industry. Could these caterpillars be harvested of their bristly hair and the material spun into fabric gold? Nope. Didn’t happen. And so, the beasts were released into the wild and our backs were collectively turned.

          The moths went “Whee, we’re free!” and started on a steady and unfettered increase to their overall population. For the first few decades, humanity shrugged this off with a big “so what?”  Who’s sorry now?

          Before I get to the human reaction part of this column, let’s take a quick look at the usual life cycle of these creepy crawlies. It’s pretty straightforward as far as moths go… eggs, caterpillars, cocoons, adults, eggs again.

          The problem lies within that one stage, the caterpillar. Many moth species do not eat in the adult stage, so enough energy and protein must be assimilated prior to that miraculous metamorphic change that takes place with the cocoon, the changing of all the body cells from a solid to a fluid and then back to a solid but in a much different configuration. This is like saying you and I can eat all we want from age 10 to 18 but then that’s it for the rest of our lives. So glad I’m not a caterpillar.

          As the caterpillar grows, it keeps shedding its constrictive outer skin, sometimes five times (each stage is called an instar). Not only is it now bigger but the colour and adornments change too. And the bigger it gets, the more food it eats in a sitting (and the larger the caterpillar poo gets on your patio).

          Then it’s a quick snooze inside a cocoon until out comes the adult moth, either male or female. The males can fly and do so; the females cannot, so they begin the long trek back up the tree to find a suitable site to attract a male and lay her eggs. Once the mating is done and the eggs are laid, both male and female moths drop dead. So glad I’m not a moth.

          Now here’s the twist… as gypsy moths are introduced to North America they have no natural controls on their populations… no predators, plus abundant food, makes for an ever-increasing population. However, in time, something has to give. When 1.2 bajillion caterpillars start feeding on a forest that has only enough leaves for 0.5 kajillion (not sure of my accuracy, but you get the drift) it boils down to simple supply and demand.

          Without enough food to go around, part of the population gets sick and does not develop well, maybe not even getting to the cocoon or mating stages. Indeed, with enough sick and weak caterpillars out there, viruses can spread like wildfire and start picking them off, one by one, a thousand by a thousand. Sucks to be them, but to the survivors it means that next year there will be enough food to go around.

          This drastic collapse is called a population crash, and it happens quite often in Nature. Not all the critters are killed, just a huge proportion of them. The survivors survive and start reproducing to build up their numbers and in 10 years or so… here we go again.   

          Which, at long last, brings me to the second part of this dissertation… human behaviour. Full transparency here: I am a human and I do not react well toward gypsy moth caterpillars.

          We humans like things that we can control, such as where to plant the landscape trees and which species are to go where. When something starts to get out of our control, mild panic sets in. We seem to be hard-wired that when a situation occurs that’s out of the norm, our brain sends out a message: “Somebody Needs To Do Something. Now!”

          And this is where I spring into action. Totally ignoring the much larger ecological world of fact and natural unfolding, I grab the blow torch. “Die, you miserable invading hairy bits of uninvited filth!” After several days of BBQing caterpillars yet seeing no reduction in the harm being done to my beautiful oak trees, I notice my Good Wife’s bemused grin.

          Good Wife is a trained entomologist (a studier of insects) and has an annoyingly large amount of common sense. She points out (as she did last year as well, if I recall correctly) that I am not killing all the caterpillars, just the hapless ones that rest on the tree trunk at blow torch level. The canopy still has thousands of caterpillars, each looking down and laughing at me as they finish off another oak leaf.

          So, what I’m really doing is easing the competition so that the survivors have lots of food and will grow big and healthy and go into the cocoon stage in good health and later emerge to make lots and lots of egg masses.

          This kind of thinking I do not want to hear as another propane bottle fizzles empty.

          If, and this is a big “if,” we all just stood back and let Nature take its course, the caterpillars would die back due to over-population, the trees would rebound next year just as Nature has programmed them to do, and all this wringing of hands and bemoaning of events could perhaps be redirected to something that actually matters.

          But I am human, and there are colonies of big, fat, juicy caterpillars staring me in the face, so it’s off to the hardware store I go for another bottle of propane. “Leave them alone? Let Nature take its course?” Ha, I laugh in your face! My mind is set. Futile effort is my middle name.

Dave’s Notebook: I'm not going to complain about our wet weather this week... my whining pales in comparison to what our North American neighbours in the West are enduring right now. Maybe we should be thinking about water conservation now?

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© 2021 David J. Hawke

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