“I was walking in my garden late one morning, when my eyes beheld an eerie sight (to tune song Monster Mash). Caterpillars … oodles of caterpillars moving south from the edge of my moon garden.
They were everywhere. There were sizes from 1/2 to 1 1/4 inches long.
Then while photographing along the south side of the weed patch, there were more and more caterpillars! These were heading south too. Some were eating.
This picture shows more details of a larger caterpillar. I stepped off the side of the weed patch — 21 yards of caterpillars. The moon garden had 5 yards of caterpillars. They weren’t moving out of anything else in the yard.
Over the next several days, I found them everywhere. A lot that went into the water garden didn’t survive. I let nature take its course. This picture shows size differences, and none of these were the size of the largest ones around.
You can tell by the droppings that caterpillars had been in here.
I started wondering what the throngs were eating and finally figured it out.
Patches looking like this got me to looking closer. I don’t know that kind this is. My mother calls it “barnyard grass.” All I know, it’s difficult to weed out of the gardens. All the patches of it in the yard looked like this.
The caterpillars’ appearance changed at they grew. I was outside one evening with my caterpillar book — Caterpillars of Eastern North America. It has roughly 400 pages of caterpillar pictures! I went through it 2 times, and none of the pictures looked like these. My husband came walking up toward the house from his archery target. I showed him the eaten grass and one of the caterpillars. He immediately said, “They’re armyworms.”
Well, apparently, armyworms can be a severe pest, especially on farm crops. The larvae grow to 4cm.
None are in my yard. They’ve pupated underground. Since we’re not in their year-round range here in southern Illinois, these won’t survive the winter. Southern populations might immigrate, and may or may not make it this far north next spring.