Cutworms are my least favorite insect. I despise them more than mosquitoes, black flies or deer flies (a close second). They live under the soil during the day. Then they come up at night and take one bite of a plant right where that plant goes into the ground, killing it. Back down into the earth they go making it impossible for you to find them the next day. Their handiwork is very evident, though. You can plant a nice six pack of tomatoes one day and have nothing left six days later.
This is what they look like.
When I come across one, I immediately feed it to my chickens.
There are a few things that you can do to limit their damage. Veggies that are broadcast or planted in rows can be surrounded by crushed eggshells. The cutworm is a soft-bodied insect and it would have a hard time maneuvering around in this environment.
When buying transplants like tomatoes, peppers, eggplant or anything else, it is wise to put a cutworm collar on the plant as you put it into the soil. This tomato plant has a tin foil one about one inch above the ground and one inch below.
This keeps the plant safe.