When I was living in Fort Frances, Ontario, several years ago I was introduced to the species of caterpillar known as "army worms". Actually, the true name is tent caterpillar. It's my understanding that they have this name because when they make a cocoon, they do it by folding a leaf over and sealing the edge with silk, so they are inside a little "tent". I'm guessing people call them army worms because they were EVERYWHERE, and because they are often seen "marching" in the same direction.
Apparently the population of this particular insect has a cycle that waxes and wanes about every seven years. It just so happened that the spring I was living in Fort Frances was the year that these guys had their big boom. They were on the sidewalks. They were on the trees. They were on the sides of the houses. If you walked under a tree they would often drop onto you. You could see them on the road, all walking in the same direction. In a nearby town cars were sliding because there were so many of them on the road. There were a couple of days in the spring when the leaves just started to come out on the poplar trees. Two or three days later the leaves were gone because they had all been eaten. It looked like winter again.
I was pretty grossed out by the ubiquitous caterpillars and resented the fact that they were everywhere. I got pretty good at flicking them off of me when they would fall on me as we were walking down the street. Sometimes they would even manage to climb under the door frame and into our apartment.
I'm not sure how we got the idea, but we caught an army worm and kept it in a jar in our apartment for a while. We named it Walter, after my companion's boyfriend. We would look at what the other worms were eating outside and bring it leaves to eat. Over time my attitude changed toward the army worms. I came to appreciate their funky beauty. They are black with orange, blue, and yellow "footprint" marks on their backs. Pretty soon I kind of felt attached to them, especially to Walter.
Walter made a tent one day and turned into an small, ugly light-brown moth. I didn't find out his metamorphosis had completed until he had already tried to fly around the jar so much that he had beat his wings apart against the jar and died. I would have let him go outside if I had known. After seeing the pedestrian brown moth that Walter had turned into, I sort of wished that he were back to being a black colorful caterpillar again.
Here is a Wikipedia article, including a picture of what these guys look like:
There are a few different species mentioned on Wikipedia, but this one looks the most like the way I remember them.