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Bad year to be a tree 2 - Operophtera brumata

Bad year to be a tree 2 - Operophtera brumata
Middlesex County, Massachusetts, USA
May 5, 2010
Size: 12 mm (approx.)
Badly defoliated small tree (IDed by John Pearson as sugar maple, Acer saccharum)

If you had a lateral view,
you would see a half-sized pair of prolegs on A5 in addition to the pair on A6 for Alsophila. The images in Wagner for Alsophila also don't show the broken dark dorsal line we see on your image and on his images for Operophtera.

I added some lateral views of other caterpillars.

I see proleg on A6, none on A5 (if I count correctly and A1 is the first segment after the hind true legs).

Moved from Geometrid Moths.

With 10,000 + species of moths in North America
or more, we are just too much of amateurs to say for certain. Maybe someone else can be more certain. We would have called all of these images O. brumata, but not with the certainty you may be looking for :(

Moved from Moths. I'm confident in family, at least.

Is there anything else these could be besides Operophtera?

Wagner talks about brumata being an introduced pest
in Massachusetts. "During outbreaks they enshroud entire trees in silk". "Under outbreak conditions, ground color may be gray-green, smoky, brown, or black."

Plant host... Sugar Maple (Acer saccharum).

Wonder if these all might be Bruce Spanworm
Operophtera bruceata, Wagner pg 210??

How are spanworm caterpillars distinguished from cankerworm (Alsophila pometaria)?

I wondered that too. A newspaper story reported concern that this could be a bad year. Do they change color from black to green? I don't have Wagner, and I don't understand what differences are important for ID.

It's almost all O. brumata here, near the coast. Apparently they are indistinguishable from photos.

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