It’s late october and you grab a branch on a Live Oak tree, expecting to feel something firm. But instead you feel…softness. And then you touch your hand to your other hand and feel it burn instantly. The venomous spines of the Puss Caterpillar is embedded in your flesh, as if someone is holding brand iron to your skin. Not a scratch from a thorn, not a bee sting. A bite from what is considered most venomous caterpillar in all of North America, but one that resembles a baby lamb.
If only it looked fierce! But that’s the point: its harmless look is its own form of defense. And knowing that may save your skin (or at least spare you some stinging pain) when out hiking or working in the garden.
How to Know If a Caterpillar Is Safe
Not all insects are bad guys; some are actualy beneficial to have around (and you want them in your garden). The ones I see most often that are easy to ID is moths or butterflies. They begin life as larvae or caterpillars, then pupate, and then emerge as winged creature we call butterflies. Most people know the names of butterflies but might need help with the larvae forms, so where do you learn those?
First, recognize that each kind of insect is picky about what it eats. By knowing the plant, you can also name the insect. But how would you do that? It gets back to knowing the native plants in any area, and there are lots in Texas, from the Hill Country to East Texas in the Piney Woods. Because each habitat will support different kinds, and the caterpillar is picky about what it eats. So if you encounter a larval form on a citrus tree down in South Texas, chances are it’s a Giant Swallowtail, a butterfly that’s good for you and harmless. It’s all a matter of knowing who lives where and what plant they eat. Once you know that, you do not need an entomology degree to tell whose it is.
An additional tip-off: When in doubt, look at the timing of the caterpillar. Spring (March-May) is prime time for Buck Moth caterpillars. Fall (September-November) is prime time for Puss Caterpillars. Is a dark spiny larval critter crawling across the leaves of your oak tree in April? That’s probably a Buck Moth. Their venomous spines branch off and can cause painful swelling and hives. Because the venom penetrates deep into skin, the pain will persist for hours. Gloves is required to rake beneath oaks in early spring.
In late summer, avoid the slug-like critters with green spots on their backsides (above). That’s probably a Saddleback caterpillar, whose spiny body is disguised by smoother surface. Their sting will burn right away and produce raised welts that look like an allergic reaction. Same goes for other brightly colored, hairy or prominently spined caterpillars: Don’t mess with them. Stay back.
The green ones with no hairs? It is fine to get up close and personal with ones like these, the larvae of the Hackberry Emperor moth on hackberry trees. Why are we seeing these insects at this time? Because there’s a life cycle and it explains everything.
First off: egg-laying females will deposit their eggs (often in groups of fifty or more) on particular host leaves, which for me are some sort of leafy thing, usually in spring here. They then hatch into small larvae (e.g., caterpillars). They eat voraciously until reaching their last stage. By this time, they is big enough to spot easily and have fully developed their defense mechanisms. That’s when I want to ID them, before they go into pupation, because after that: no more stinging spines, just moths/butterflies.
If you have a run-in with any of these toxic creatures, always remember safety first. If you encounter a Puss Caterpillar, do not rub the sting. Rubbing will push its microscopic spines further into flesh and make the venom spread worse. Gently remove the spines with adhesive tape. Apply ice for pain relief and swelling reduction. The resulting hives and itching are treatable with antihistamines. For severe symptoms such as trouble breathing or chest pain, seek medical help ASAP.
Learning about local habitat is key to ID-ing Texas caterpillars. Start with the plant, then look at the time of year, and finally look at the creature itself, including its colors, spots, bumps, and more. All but a tiny number… Mostly easily spotted if you know what to watch for, are harmless, and most are actualy beneficial, helping sustain the food web by supporting birds. A few is directly harmful to people, though. And knowing which is which protects you, too. Be prepared with some tape, go easy on the hairy things, and enjoy as larvae become winged adults.