I believe it's the larvae of a tiger swallowtail butterfly:
http://www.google.ca/search?q=...

Will have to look a bit more to figureo out which species. Did you find it here?

Thanks Lori. Yes, it was in our garden September of 2011.

It appears to be a Western Tiger Swallowtail (Papilio rutulus), based on it being green rather than brown as in Canadian Tiger Swallowtail (P. canadensis)... I don't know much about butterfiles and I don't know if this is reliable distinction, so just a guess on my part. The larvae of both feed on poplars, willows and cherries.
Terrific find! It always seems strange to me how few butterflies and moths, or even insects in general, there are in Calgary. Our yard has ample bloom all through the season and yet butterflies and moths are few and far between. A few years ago when the Painted Ladies had their big irruption, was the only time I've seen something like a "normal" number of butterflies here.

It was really neat to see that little guy. The markings were very cool. We had put it in the neighbour's crab apple tree. I agree, there are very few butterflies, moths, dragonflies and humming birds. We see many more at our farm and there are only wildflowers there. Thanks a bunch for researching the info

Great shot, Joanne! One of my favorite caterpillars!

Not nearly as attractive as yours, and the photography is way inferior!! I saw this one the other day, it was the only thing greeenish on the forest floor. I have no idea what kind it is.

Joanne, it could still be a Papilio canadensis (Canadian Tiger Swallowtail) caterpillar, because they ARE green. The different tiger caterpillar start out dark, then look somewhat like bird dropping, then they turn green. The day or so before pupation, they darken and are brownish or dark brownish. I googled Papilio canadensis images and this is what turned up. BTW, the key to ID on the tiger caterpillars is mainly the eyespots, once they develop eyespots.
http://www.google.com/search?q...
I've only raised two species of tiger...Eastern Tiger Swallowtail and Two-tailed Tiger Swallowtail.

wildflowers said:Great shot, Joanne! One of my favorite caterpillars!

Not nearly as attractive as yours, and the photography is way inferior!! I saw this one the other day, it was the only thing greeenish on the forest floor. I have no idea what kind it is.

This could be an Imperial Moth cat. see:
The thread "What cat is this? Help IDing please." in Gardening for Butterflies, Birds and Bees forum

And:
http://schmidling.com/impmoth....