This Saddleback caterpillar (Acharia stimulea) showed up at a master naturalist field trip I was co-leading last year. This is one of our largest slug caterpillars (they're called this because of the way they move in a gliding fashion, with no legs showing), but you can see how small it really is. The sting hurts to be sure, but is not that big a deal for most folks and I was not afraid of getting stung. They're neither aggressive nor quick. There's been a lot of sensational info on stinging caterpillars, but they're mostly not a problem around here unless you happen to be allergic (which can happen if you're allergic to anything and is rare regardless, but it can happen, as my wife can attest to from an encounter with a stinging Barboso caterpillar in her home country of El Salvador that had her hospitalized a week).
Most members of the slug caterpillars, family Limacodidae, are armed with stinging hairs. You can actually see the stinging spines on this one. This is considered the most powerful sting among our native slug caterpillars. Because they use their stinging spines in the construction of their protective cocoons, even these can sting. You can also see the warning colors and the saddle-marks that give them their name.
Their stinging abilities do not protect them from all predators though, with wasps in particular preying on them. Braconid wasps insert their eggs into them and the wasp larvae feed on the inside, leaving the vital organs until the last. The walking caterpillar is a zombie. When the white little wasp cocoons show up on the outside of the caterpillar, it is basically dead but still moving. I've also seen paper wasps bite off the stinging spines so they can take them back to their nests to feed their young safely.
Just today I found a Saddleback crossing the entry road to one of our nature centers. Having heard that they won't sting when gliding over you, I decided to test that theory. So I let it crawl onto my finger for about 20 minutes and can attest that this particular one at least did not sting me.
|Apparently Saddlebacks can crawl on you without stinging. The stinging hairs are pretty evident along its back however.
These beautiful caterpillars are polyphagic, meaning they can eat a lot of different plants. I've found them on corn, maples, oaks, elms, apple trees, even English Ivy (which almost no other native creature eats). They've also been reported feeding on the leaves of blueberry, beans, buttonbush, cabbage, citrus, grasses, grapes, linden, ash, dogwoods, cherries, iris, viburnums, and asters. The worst experience I ever had with them was when I bumped into some stinging nettles and of course got stung. A second later I got tagged again by the Saddleback that I had accidentally picked up that was feeding on the stinging nettle. A double whammy.