Matt has gotten me distracted by bugguide.net on occasion - here's a snippet of what can happen when people contribute to citizen science.
When we were in Kerrville at the end of September, we found and photographed a large, green caterpillar on the house where we stayed. Unable to come up with an ID on our own, Matt submitted the image to bugguide, where some helpful folks narrowed the ID.
Drab Prominent Moth (Misogada unicolor) caterpillar
...check out the link above - it has fake antennae/eye stalks on its rear end! Pretty snazzy, eh? So if a bird/bug aims for what it thinks is the head, it's only a bit off the rump that goes missing. Kind of like the hairstreak butterflies and swallowtails as well - better to lose a showy wing extension than your head! If the critter is thought to be a slug, with the fake eye stalks, it's still doing pretty well... but a green slug mimic? Pretty crazy.
Here's an adult Drab Prominent Moth from bugguide:
Another of Matt's previous caterpillars, a Hemileuca is also in the bugguide archives, but it is a far fancier creature and looks like quite the formidable opponent!
It's interesting to see how the internet is making ID a rapid, paperless process. Photos and human opinions are now outweighing wordy descriptions and otherwise scarce (as well as incomplete) resources. Yet we still have so far to go.