Q: I think something stung me while I was trimming chewed leaves off of my plant. I was expecting a wasp to fly out, but all I see is this insect that I think is a caterpillar on the bottom of a leaf. Could this be responsible?

A: Yes, this is a saddleback caterpillar, and they are one of our handful of species possessing irritating or stinging hairs or hollow spines on their body. They mature into a moth with a medley of chocolate-brown hues, which is native and widespread in Maryland. I find the caterpillars to be quite nifty-looking, looking like some sort of saddle-blanket-wearing terrier with headlights or glowing eyes on one end. (There are a pair of prominent pale yellow dots on its rear end not visible in this photo.)

They have such a wide host plant range, that it’s hard to predict where you’ll find them. In my experience, they find you, as you puzzle why the leaves you brushed against are giving your skin that stinging sensation when you haven’t touched a stinging nettle plant. When I’ve run across them, one or more saddleback caterpillars have been feeding on heuchera, spicebush, blue holly and Redosier dogwood.

Young caterpillars may congregate and feed near each other, though older caterpillars tend to be solitary. They don’t get very large; about an inch in length before they are ready to stop eating and form a cocoon.

Leaves with chewing damage don’t necessarily have to be trimmed off unless they have other damage issues, like an overlapping fungal or bacterial infection that’s damaged most of the leaf. Otherwise, chewed leaves can still photosynthesize and feed the plant. If you trim perennials and shrubs in summer for any reason, use caution and watch where you put those hands if you don’t have on gloves.

The saddleback’s sting is reportedly comparable to a bee sting in terms of painfulness, and generally subsides on its own over time (a few hours or less). Always check with a medical professional, but barring an allergic reaction or acute sensitivity, it’s an unpleasant but not otherwise high-risk experience. Since venom-filled hollow spines on the caterpillar could have broken off and lodged in your skin, wash the area well and, as with cactus bristles, use a piece of adhesive tape to pull out any lingering spine pieces.

No management of saddleback caterpillars is needed, and a population chewing on a plant one year won’t necessarily mean they’ll return the next. If you can’t avoid the plant until the caterpillar matures and wanders off, then snip off the leaf it’s sitting on and place it in an out-of-the-way spot; odds are it can find another suitable plant species to munch on that won’t bother anyone.

Q: My basil plants have brown bumps on the lower part of their stems, and my diagnostic app said they could be scale. How do I save my plants? So far they seem to be growing well.

A: Apps vary in how accurate they are for any given diagnosis, and the more likely explanation in this case is that the bumps are adventitious roots. Scale insects on basil are rare and would be found more spread-out, or even on foliage. Adventitious roots are simply roots that form on parts of a plant that don’t normally grow roots, and the lower portions of a main stem is a common location. Their development can be normal or a response to other kinds of stress.

Adventitious roots do not typically finish developing into fully fledged roots, and instead remain as firm, brownish or pale green nubs clustered on the stem. If the bumps on your basil stem do not rub off easily and are not associated with honeydew (a sticky, clear residue), then scale insects are not likely. In comparison, adventitious roots will not come off unless you scrape them away, which will injure the stem in the process.

Don’t worry about removing them, though their presence might suggest that the plants are being kept too damp. Plants that commonly manifest adventitious root development when stressed include basil, rosemary, lavender, tomato and pepper, though this can also depend on genetic predisposition from one cultivar to another.

University of Maryland Extension’s Home and Garden Information Center offers free gardening and pest information at extension.umd.edu/hgic. Click “Ask Extension” to send questions and photos.