Subject: Slug caterpillar
Geographic location of the bug: Ionia mi
Time: 11:51 AM EDT
Your letter to the bugman: This was on my boat cover this summer which was parked under some walnut trees. Please help identify.
How you want your letter signed: Ben
You have the Slug Moth Caterpillar Limacodidae correct. This is a Skiff Moth Caterpillar, Prolimacodes badia, and here is a BugGuide image for comparison. Your individual has much larger tubercles that those on most pictured specimens. According to BugGuide: “larvae feed on leaves of wide variety of trees and shrubs, including birch, blueberry, cherry, chestnut, Hophornbeam (Ostrya virginiana), oak, poplar, Sweetgale (Myrica gale), willow, and others” so we suppose “others” can include walnut.