Dogbane Saucrobotys Caterpillars

Subject: Larvae identification
Location: Southwest MI
August 31, 2016 12:18 pm
I have several tent nests on the Prairie Dogbane (I believe this is the plant, though my MIL says it’s milkweed) growing in my front yard. These are silky nests on the leaf ends of the plants, and they aren’t found on any other plant species in my flowerbeds. The eggs are tiny and dark, almost black, and the larvae are less than an inch in length, orangish in color, with black spots and no hairs. The larvae may still be immature, though there were several sizes in the nests, and these were the largest I found. Can you identify these insects? Are they beneficial or pests? Thanks for your help!
Signature: Val

Dear Val,
Thanks for providing the name of the food plant, because we didn’t have a clue about the identity of these caterpillars, but we quickly identified them as Dogbane Saucrobotys Caterpillars, Saucrobotys futilalis, thanks to this image on BugGuide.  According to BugGuide:  “Caterpillar feeds on dogbane, Apocynum species, including Apocynum cannabinum (Indian Hemp), and on milkweeds, Asclepias species, including butterfly weed, Asclepias tuberosa (Maryland Moths). Larvae make conspicuous silk nests on their host plant.”