Here we have an opportunist caterpillar. It must have come in with food I provided for other caterpillars. By the time it was discovered, it was about 1cm. (Very small!) It is a generalist (eats a variety of plants) and doesn't have much visible setae. Somewhat seems to match Yellow-striped Armyworm p.433 in Wagner's. It does appear to have eyespots amid its stripes.

In the follow-up photos you will see as the caterpillar grows into larger instars that the eyespots (or significant black spots) are first at the anterior end and later at the posterior end. Also the yellow stripe in this individual becomes less noticeable at 5cm.