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Gypsy Moth

This year seems to be a good year for Gypsy Moths and a bad year for people who love their trees! Never seen one? This might be the best time to find them. Look for a light to dark brown, medium-sized moth flying around in a seemingly erratic way. These are the males. They are ‘sniffing’ the wind while being drawn to the female by pheromones she releases. But let’s step back for a moment and talk about how they got here and why we care, before we delve more into their eruptive life cycle. Originally they were accidentally released near Boston in 1868, and then they spread throughout much of northern and west-central USA and central and eastern Canada. There were few predators to stem their expansion and many birds and other organisms hadn’t developed mechanisms to feed on them yet, so spread they did! Flash forward, in the 1970s and 1980s, they were a huge problem as they emerged in the millions in many areas including Durham and the Kawarthas. Huge swarms of them could be seen feeding on virtually any type of tree, but favouring maple, oak and aspen. They are called outbreak species, and may be present for two or three years, then seemingly disappear. Longer events are the ones most devastating to trees. As trees are defoliated year after year, they weaken and can die or other insects and diseases can attack the tree. But they rarely seem to cause the widespread fatal damage the Emerald Ash Borer causes. The female is a white moth with small black flecks on the wings and is flightless. Right now you can see her sitting on the bark of a tree with a pale sandy coloured fuzzy looking mass, underneath her. This mass is her eggs, 100 to 1000 of them, that will survive the winter. In April they will hatch and start to disperse by a mechanism known as ballooning, where they move to the ends of branches and let the wind carry them to a food tree. They grow rapidly, shedding their skin several times, five times in males and 6 times in females, as they gradually, over the next 6-7 weeks, get larger. Newly hatched caterpillars are small and are often overlooked. The caterpillars are grey with small tufts of hair along their sides and several diagnostic pairs of red or blue dots (tubercles) on their dorsal surface, which are blue towards the head and red along the middle and rear of the back. As they grow larger, they may start feeding more during the day and that’s when we often notice them. Finally they enter a pupal stage near the host trees, choosing rocks, tree trunks, buildings and other hidden places. This is the phase where they will transform over the next 10-14 days into adult moths, which will carry out the reproductive part of their life cycle. From a human perspective they can be irritating because of the damage they do, but also the hairs of the caterpillars can be irritating to human skin. So what should you do? This is a tricky question and it really depends on the value you put on your trees and the environment in general. Most healthy deciduous trees can survive one or two seasons of heavy defoliation, so doing nothing can be an option. Their rapid reproduction rate is also beneficial to other wildlife because many birds and other animals can now feed on them. I did a study in the 1970s and found over 70 species of birds feeding on the larvae in the Peterborough area. Insects are already in serious decline throughout the world, so killing insects for the sake of killing them seems ill-advised. The use of insecticides is indiscriminate, and will kill many beneficial insects as well. Many biological organisms, from parasitic wasps, fungal and viral pathogens, birds, mice and shrews are doing their part to stem the spread naturally, so nature is hard at work! So each of you will individually have to decide what to do. For me, I’ll let them live and be part of my ecosystem. Geoff Carpentier is a published author, expedition guide and environmental consultant. Visit Geoff on-line at and on LinkedIn and Facebook.

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