As I was weeding the other day, I brushed my arm under an iris leaf and thought I'd cut myself. Thought that for about a second anyway. That's when my arm began burning furiously and I looked to see a green and brown spiky caterpillar hanging from the underside of the leaf. Alarm bells going off in my head, I ran inside to run my arm under cold water, then downed a couple of benedryl and slapped an icepack on it while I quickly googled "stinging caterpillars." There it was, a saddleback caterpillar (this image from About.com.) See all those little spines? They use them to inject a powerful venom.
I quickly researched suggested treatments. My favorite site had step-by-step instructions with photos, including one telling you to calm the person who was stung. So after I settled myself down I followed every other suggestion - repeatedly put pieces of tape on the affected areas to pull out any remaining spines, wiped my arm and hand down with lemon juice, applied a paste of baking soda and water, and kept ice on it. And still, it was, as one article put it, "like somebody lit you on fire." It was described also as "a bee sting times a hundred." Truly, it was remarkably painful - it managed to get both my hand and my arm and they hurt intensely for more than an hour. Several days later, I still had a red rash where I'd been hit. I asked my friend this weekend if he'd ever heard of them and he said, "Yes!" and went on to describe the pain of accidentally grabbing a leaf which held one. He said they call them packsaddles around here.
When I went back outside to take a photo, my hands were still shaking and the picture is blurry. But this is the perp, after I knocked him off the leaf and scooped him up with a trowel. I normally leave bugs to their own devices as long as they stay outside. Bumble bees are allowed to hover by my head as I work, lady bugs can crawl on my shirt, inchworms are free to measure my arm. But this one? I killed the little fucker.