Donna and I were lucky a couple weeks ago while at the park with the dogs. We were walking back to the car from the water area where Willow was swimming when we came upon two people hunched over something in the trail. When we got closer, we saw a giant green caterpillar with bizarre head spikes. Everyone was afraid to touch it, because the spikes looked pretty nasty (an effective defense, indeed!). The dogs were only semi-curious, but we kept them away just in case. It was crossing the trail, one frequented by dogs and bikers, so the two people hunched over it were trying to protect it as it made its way to safety. I took a couple shots, which didn’t come out perfectly, but should still give you an idea.
These caterpillars turn into Royal Walnut Moths (aka Regal Moths), which are quite beautiful. They are typically found in late summer, growing during the caterpillar (larvae) stage for about 40 days before wandering around looking for a place to burrow in order to pupate over the winter. The moths are usually found during mid-summer. It turns out the Hickory Horned Devil is quite harmless, so we could have picked it up with no worries. But, better safe than sorry.