Insect and Spider Identification: CLOSED: What is this caterpillar?, 1 by Sequoiadendron4

Sequoiadendron4 wrote:
This caterpillar is a sly one as it's very hard to see on a quick pass. These guys are on a volunteer hesperis matronalis and I noticed the leaves were quickly getting defoliated. I had some seedling hesperis growing in pots that faced a similar phenomenon a couple months ago. All of them were quickly defoliated but I never noticed the culprit. Now I think I just wasn't looking hard enough. Anyone have any thoughts?