Geographic location of the bug: NW corner Connecticut
Time: 07:15 PM EDT
Your letter to the bugman: Looking for an ID. Consulted the Exec Director of Audubon here in CT and he did not know.
How you want your letter signed: Lori Welles
We thought this was going to be an easy identification, but more than an hour later, we can state unequivocally that we were way wrong. Our mistake began by not looking at your image that closely, and thinking we were trying to identify one of the Hooded Owlet Caterpillars in the genus Cuculia, but after ponderously searching BugGuide, we realized we were wrong. Our search next took us to The Moth Photographers Group where the Zebra Caterpillar looks similar, but not the same, and the Scribbled Sallow Moth Caterpillar pictured on The Moth Photographers Group and the Toadflax Brocade Moth Caterpillar, also pictured on The Moth Photographers Group also looked similar but not the same. The solid black head on your individual and the round yellow lateral spots were quite distinctive and not found on any caterpillars we could locate. Something about the head did not seem right, so we decided to count prolegs, and there appear to be seven pairs, which caused us to think this must be a Sawfly larva. According to ThoughtCo: “Caterpillars may have up to five pairs of abdominal prolegs (tiny limbs) but never have more than five pairs. Sawfly larvae will have six or more pairs of abdominal prolegs.” Once we searched for Sawfly larvae, we came to Wildlife Insight where we found images that match your individual that are identified as Diprion similis. Armed with that information, we returned to BugGuide and located matching images of the Introduced Pine Sawfly larva, but the individual in your image does not appear to be eating pine. Upon what plant did you find it? According to BugGuide: “hosts: pines (Pinus); 5-needled pines (Subg. Strobus) are preferred, but others may be infested as well.” This BugGuide image contains the information: “This one was on a poplar plant, and the other was eating oak leaves.” Thank you for submitting this challenging identification request.
This was feeding on Cosmos. Glad it was a challenge as many friends including the Exec director of Audubon here in CT. could not ID.
Welles, The Ballyhack