The tomato plant has a horned grub on it, and you know what? It’s more than just a bug eating your dinner. You’re seeing a battle of biology playing out in your back yard, usualy immediately after the monsoon. In July-August, everything suddenly becomes lush. It turn into feeding grounds for larvae who suddenlly seem to multiply overnight. They change entire look of the landscape. Suddenly, what was mostly brittle scrub becomes lush (and then they eat it). Panic turns into understanding, then it becomes curiosity or maybe even management.
More than a thousand different types of butterflies and moths lives here in the Sonoran Desert, meaning we have hundreds of distinct caterpillar shapes crawling around suburban edges, mountain meadows, and wash bottoms. Of course, most folks only observe those that makes themselves noticeable. This includes things like tobacco or tomato hornworms, which chew leaves off their favorite plant like nightshades. If you study the chart above, you’ll begin to see the complex network of relationships between caterpillars and their host plants.
Learn About Garden Caterpillars
Some creatures, like the white-lined sphinx caterpillar, do an excellent job of camouflage, changing from nearly black, to bright yellow, to bright green as they advances in age and diet. Grapes and willow herb form part of its food chain, and you’re likely to stumble across one camouflaged in plain view (until it stretches itself a few inches more). So where do you begin to learn what’s what? You can’t separate larvae from the plants they eat without finding half the answer. With a little sleuthing, you can identify these creatures by who is hosting them: The pipevine swallowtail caterpillar is dark reddish-black with orange spines and lives only on Aristolochia vines. By feeding on that particular foodplant, it has absorbed toxins making itself bad-tasting to predators. So if you don’t grow pipevine in your garden, forget about seeing this one, no matter how much you look.
The same is true for the two-tailed swallowtail because it depend on ash trees growing along riverbanks. What does this mean? It means that learning to know your flora is realy the key to knowing your fauna.
It is a short window of time. Biological rush hour comes during the monsoon season. Larvae take weeks to mature, but warm humid evenings and new leaf growth that follows each big storm send things into overdrive. Moths, including many cutworms and beautiful sphinx; emerge from cover in days to dine on tender leaves. Just when? It happens anytime the air feels sticky (and that’d be dawn or dusk, since midday heat forces them underground or back to heavy shade). A headlamp would of come in handy if you’re hoping to spot any yourself, though water bodies, where moist air persists longest (are prime places to begin your search).
With desert larvae, safety first. No matter how adorable they may seem, avoid touching any hairy (bristly) caterpillars with exposed skin; some are armed with so-called urticating hairs that will sting your eyes and create a nasty rash. Such is the case with the spiky black and orange bordered patch caterpillar (above), which eats on sunflowers gregariously, but should be admired at a safe remove. Appreciate the elaborate patterning and protection systems, but don’t tempt a face-to-face meeting. Ditto for all other unknown larvae: Wait till you’re sure what they are.
That’s what all those various-looking caterpillars is doing: The life cycle explains how they change forms, sometimes quite dramatically from one stage to another. Young ones (early instars) is small and often nothing at all like what they will become when full grown, and you may not know what to call them, making ID tricky. Then they quickly outgrow their skins several times, then stop to wander around looking for a place to pupate. Butterflies creates exposed chrysalides on plants; moths go down in the dirt or make themselves a cocoon. And then this: Metamorphosis happens here, transforming a machine made for eating leaves into an airborne pollinator that keeps the desert ecosystem humming along.
Identifying beneficials and not-so-beneficials help pay big rewards in garden health, but it’s a skill developed over time. Certain larvae (such as fall armyworm) presents a serious threat to crops; others aren’t harmful or even seasonally present. Knowing their host preferences and other behaviors will help you determine when to let nature run its course, and when to intervene.
Next time you encounter a striped green larva on your pepper plant, pause: What is it? It may be the butterfly to come, another kind of quiet charmer in a dry landscape.