Stinging Caterpillar Cautionary Tale

Last week I was watering my potted plants on the back porch when a small patch on my arm began to sting and burn similar to when I've been stung by a wasp. I had not been near a wasp nest that I could tell however so I was perplexed. I finished watering and took a closer look at my arm. I had about three distinct raised areas and some redness similar to what I'd expect from three close proximity stings but without a telltale center spot where a stinger would have stabbed. I could not imagine missing seeing one very active or several wasps. That coupled with the lack of stab points really had me wondering what was going on. The reaction I was having was similar enough to previous insect bites or stings that I took an antihistamine as I had been previously instructed by my doctor in such an event and I dabbed some aloe vera gel on it. One or both treatments helped take the edge off of the symptoms but I still had uncomfortable welts the next morning.

It was a day or two later that I discovered what likely happened. Again, I was watering my plants and noticed a lot of frass near the base of my burr oak sapling's pot and that some leaves on my little oak had been munched. I looked for the culprit and found some very camouflaged caterpillars. When I saw them I had an aha moment about my mystery skin reaction. The green caterpillars had a red and white stripe running down their sides and their back and sides were covered with feathery looking branched protuberances. I suspected these "feathers" were likely the source of my pain a couple of days ago. Based on when I started to feel the sting, I surmise that I brushed against a burr oak leaf while watering and unbeknownst to me, also one of these green caterpillars.

I grabbed my camera and took some pictures so I could identify them. Then I clipped portions of leaves and dropped the caterpillars I could find in a box. I had nine of them by the time I was done. I relocated them to a tree that could withstand a bit of munching better than my little sapling. The next day I found I had missed one so I relocated it too.

The internet is a wonderful thing. I was able to find out pretty quickly that the feathery green caterpillars would become Io moths and yes, they are a stinging caterpillar. The tips of those feathery protuberances are actually tips of spines that transfer venom to what they come in contact with, like my arm. Not all feathery or hairy caterpillars are venomous but better to err on the side of caution and not find out the hard way by touching them.