Connecting Lake Simcoe's Community

Hungry invaders munch through forest canopy

         2020 06 27 gypsy moth pic By David Hawke -- The gypsies are back in town!

Like the wandering groups of old, a band of colourful characters has quietly moved in to the neighbourhood and set up camp in the nearby woodlot. However, rather than provide fortune telling services, these gypsies are busy defoliating the oak trees.

          I refer of course to the gypsy moth caterpillars that have appeared in high numbers this year and have shown up across the county on trees, patio decks and furniture, walkways, and hitching a ride on your jacket. They may be tiny when they first begin their ‘walk about’, but in no time at all they can become as big as your little finger. And the forest canopy will diminish at a similar rate.

          Gypsy moths are foreigners to North America when looked at from a natural establishment point of view. This species, which is native to Europe, Africa and southern Asia, first arrived on this continent in 1869, being noticed at that time in Massachusetts. It probably arrived as an egg mass stuck on a wood pallet.

          So that’s their back story… why be concerned about them now? During the larval part of their life cycle (more commonly known as a “caterpillar”) they, like all caterpillars everywhere, eat a lot. Some species of moths eat very specific plants; others, like these gypsies, eat a variety of both hardwood and conifer trees. Now that’s too bad in itself, the trouble begins when there is a year when their population explodes and they number in the hundreds per tree. All that nibbling and munching soon has the tree looking a tad naked.

          If we humans (well, some of us anyway) are going to wage war against gypsy moths to protect the oak trees, how best to go about it? As the saying goes, “know your enemy.” From that idea, an arsenal of equipment and an array of techniques have been utilized over the years, but with limited effect (which, if you think about that, is common with all war-like plans).

          Starting with the emergence of itty-bitty caterpillars from the egg mass, they spend more time marching than eating. Up the tree trunks they quickly go, out on the branches they crawl as fast as their little legs will carry them… and then they wait (see, I told you it was war-like). What they are waiting for is a strong breeze, not too light and not too strong.

          When just the right velocity of air currents sweep across the landscape the little caterpillars drop from the branches on a thread of silk, like commandos rappelling from overhead helicopters, and they get caught up in the breeze, break the thread and are then carried to new places. This is called ‘ballooning’ and is the same technique used by some spiders for dispersion. As the breeze comes across your yard, the air-borne caterpillars drop onto your patio furniture, your clothing, and of course your beautiful landscape trees.

     The little invaders are hungry, and as they will grow and shed their skin several times in the next couple of weeks, they need nutrition and lots of it. That’s where the leaves come in to play. Young caterpillars feed during the day but as they get older (and larger) they switch to feeding at night, and spend the day resting in clusters on the east side of the tree trunk (see accompanying photograph).

          As they grow, the fuzzy bristles that cover their body become stiff and act as a protective coating to keep insect-eating birds at bay. The bristles can cause a stinging sensation in human skin, so when you brush the disgusting creature off your jacket, you pay for that.

          Once they become big and fat, the caterpillar creates a shelter of silken threads on the side of the tree, or your garden shed, and turns into a cocoon. A short time later out comes the adult moth, wings and all. The moths do not feed, they just look for mates and lay eggs. Male gypsy moths can fly, the ladies cannot. So, the girls hike it back up the same tree they grew up on, while the lads flit about seeking new friends across the neighbourhood.

          The eggs are laid in a light brown matt of protective material (made from the bristly hairs from the female’s body) that will keep the eggs (numbering several hundred in each mass) safe from rain, snow, frost, ice and egg-eating insects. The following spring, they hatch, and the cycle of hurry up and wait begins all over again.

          Now comes the curious part, as some years there are gypsy moths literally everywhere, and other years you will be challenged to find any at all. This fluctuating population cycle is well known to foresters and landscapers. Like the legendary human gypsies, you never really know just when or where they will show up, but sooner or later they will.

          Forestry folks conduct gypsy moth egg mass counts, trying to determine where the next outbreak will occur. This is partially for to determine preparation of control methods, but also to know where the human population will rise up in outrage and demand that ‘something needs to be done.’ Informational brochures, flyers and social media posts are held at the ready.

          In years of high numbers, the humans battle the moths with everything from chemical sprays to blow torches, scent traps, the release of other insects to eat the caterpillars and burlap bags tied around tree trunks (to lure in the night crawlers where they can be squashed the next day). Yet, if one reads the reports, there have been few if any actual tree deaths caused by gypsy moth defoliation. Yes, the tree’s growth may be stunted a bit that year due to lack of leaves, but next year things should be back to normal.

          This year, the gypsy moth population is high. Next year, they may be all but non-existent. Cycles happen. We can but live through it. If you chose to engage the enemy, know that the thrill of small victories will be short-lived.

Dave’s Notebook: This wonderful summer weather has settled upon us in fine style. I hope that you find ways to enjoy being outdoors without compromising the pandemic protocols (which can be a pain to follow at times... but it is so essential for us all to comply).

© 2020 David J. Hawke

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