Forest tent caterpillars have always been around

In 1834, explorer Paul Kane recorded “. . . the trees on each side of the river and part of the Lake of the Woods, for full 150 miles of our route, were literally stripped of foliage by myriads of caterpillars.
“This scourge extended to more than twice that distance.”
He was talking about the Forest Tent Caterpillar (Malacosoma disstera). This is one of four tent caterpillars, and the only one which does not build a tent.
The adult insect is a relatively innocent-looking small moth, brownish with a mottled appearance. You would never give it a second glance. It lays its eggs–several hundred of them–in bands around twigs.
Usually laid in July, they don’t hatch until the following spring.
The tiny caterpillars develop entirely within the egg. To keep from freezing, they have the ability to turn some of their body fluids into a form of glycerol, an anti-freeze much like that in your car.
When they do break out of the egg, the tiny caterpillars start feeding and growing–to about five cm (two inches) or so.
The Forest Tent Caterpillar doesn’t make a tent but they all feed together, and in the evening, or if it gets cool, they clump together in a thick band on the trunk or main branch of a tree.
This insect is not too particular about what it eats. Poplar, birch, willow, and maple are all fair game, along with a great many other broad-leaved shrubs and trees. They very seldom go after evergreens, though, which is a good thing for us.
The Eastern species has a much more specific appetite–it goes for apples, cherries, and so on.
The caterpillars are bluish-grey, sometimes nearly black. Down the back of each is a line of small white, keyhole-shaped dots, quite different from the other tent caterpillars.
These are with us for perhaps six-eight weeks altogether. They end up spinning cocoons, often among the leaves (if there are any left).
A pupa is formed inside the cocoon, and, in a couple of weeks, the adult moth emerges. After mating, the female goes off to find the right kind of tree to lay her eggs on.
Quite often, they will strip a tree of all its leaves. In heavy infestations, the poplars take on the appearance of winter. Mature trees will usually recover, though, growing a new set of leaves in the latter part of summer.
The caterpillars have a tendency to leave a tree after a while and head off somewhere until they run into something else good to eat–a tree or a shrub. They climb up on things in their path–your house, garage, barn, tractor, or car.
They will cross roads, and are sometimes so numerous that they make the roads slippery.
There are some controls but these are only used in small areas, like your garden. Keep your eye on fruit or ornamental trees, and spray the caterpillars as soon as you find them.
There are “contact” sprays, which kill the caterpillars after it gets on its body. There also are some stomach insecticides, which have to be eaten to do the caterpillar in.
A few years ago, there was a great outbreak, which certainly affected Northwestern Ontario a great deal. This was a very large one, all the way from Winnipeg to Peterborough in southern Ontario.
These outbreaks occur in some sort of cycle, about every 10 years or so.
Don’t worry too much. After a year, or maybe two, the infestation collapses on its own.

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