Caterpillar ID?

[Allyn Weaks]

A friend from Omaha Nebraska asked me to post this request for a
caterpillar ID.  A couple of days ago her dog ate one end off of a very
large caterpillar, and after a rather brief look she tossed it over a fence
to keep the dog from getting his prey back.  The following is the
description as far as she can remember:

>It was getting dark, but it was BIG, very dark green, with fairly large
>white eyespots (outlined in black??) on the end that was left, I think the
>feet were black, and they were all close to the end that was left, like the
>kind that raises it's upper body off the stalk and tries to pretend it's a
>leaf when you blow on it (tomato hornworms.) We also have sphynx moths on
>the crab, but this was a lot bigger, and much darker green. It may have had
>a black racing stripe on both sides below the midline. It was still moving
>around when I put it over the fence into the weeds by my neighbor's cable
>box so the dogs couldn't get to it.
>
>No knobs, the skin was very smooth and there weren't any protrusions, but
>there may have been on the end that Snow ate. It was thicker than my thumb,
>and the part I had (almost certainly most of it) was about 4 inches long.

Some more details on her location and habitat in case it helps:

>I am in the NW part of Omaha, Douglas County, Nebraska in a
>suburban area.  We have a large stand of the native 8' sunflowers
>drying off and going to seed (much to the annoyance of our carefully
>grassed neighbors) and the critter was in the grass just outside the stand.
>It may have been on a sunflower stalk that fell or it may have been under it. 
>
>It might have fallen or been pushed out of the fence weed (Parthenocissus
>quinquefolia) too. Under the sunflowers is some birdseed plant - it grew
>from birdseed and there's a lot of it, I think it's Polygonum
>lapathifolium. Under that are violets, and daylilies. 
>
>The rest of the yard is grass and clover, and whatever tolerates mowing. We
>don't use pesticides or herbicides, although our neighbors use enough for a
>medium-size third world country. This used to be corn (what else?) but was
>probably originally tall-grass prairie. It's the outer edge of the Missouri
>river valley, and the Big Papillion <G> Creek runs through the park east of
>us.

If anyone has suggestions for an ID of this particular beastie, or good
references for caterpillar ID, and sources of photos of NA caterpillars in
general, we'd both be grateful.  I have already directed her to the Lep
Society homepage and photolinks at Furman University, but if there are any
useful books or other helpful sources for her area that would be a help
too.

Many thanks for any hints.
-- 
Allyn Weaks  allyn at teleport.com
Seattle WA, USDA zone 7/8
Pacific Native Plant Gardening: http://www.teleport.com/~allyn/natives/