There it is: A milkweed leaf you pull back reveals a distinct pattern of white, yellow and black bands. It is unmistakable. It’s a monarch caterpillar, perhaps the world’s best-known insect.
But take another glance around the coast, or into your own garden; and you’ll discover a much larger world different than simply butterflies in migration. In fact, there are far more then 250 kinds of moth and butterfly larvae crawling across California, from high Sierra meadows down to its sun-baked dunes. Knowing the identities of those creatures isn’t mere academic knowledge for the naturalist, but rather the secret to knowing if your garden thrive or if it’s besieged by hungry pests that can strip a tomato plant within days. Here’s how to make sense of all this diversity (above).
How to Identify Garden Caterpillars
The breakdown begins with their life cycle, which include more than just caterpillars. A caterpillar is not really a caterpillar, it’s a larva! Its sole job is to eat. It hatches from an egg, eats a lot, then eventualy forms its cocoon/chrysalis and pupates. That process give you insight into where they are in time and why one may have such a different body form from another. Sometimes you find yourself looking at a very small, cryptically-colored dot of animal that bears no resemblance to the hairy and bumpy specimen it turns into a few weeks later. Those body changes is called instars. Many folks mistake insects for another species because of these instars, thinking they are different if they don’t match up. Just growing pains!
The change of swallowtails is especially dramatic. Some of these amazing species is featured on the chart: the bright orange-spotted Anise Swallowtail and the Western Tiger Swallowtail. The Western Tiger Swallowtail’s early stage looks just like bird poop to fool hungry birds. All of these possess an osmeterium, which is a bright orange forked gland that unfurls when threatened and emits a stinky odor that even birds cannot stand. It’s a smart bit of evolution, since most predators don’t want to have to clean up after themselves. This is why the bluff works.
And then there are the milkweed experts like the queen and monarch caterpillar (and others); those who store toxic compounds gathered from their foodplants and advertise “don’t eat me” by sporting garish colors. The message is truthful; they’re indeed awful-tasting… And fastens itself in the minds of birds, who soon learn not to mess around.
The caterpillars of some brush-footed butterflies (above) depends on camouflage or even a group-living lifestyle. Others are very protective, as we’ve seen. However, not all larvae goes this far. Moth caterpillars has their own tricks. When disturbed, the Woolly Bear simply tucks itself tightly into a ball to protect itself with its wooly bristles (though its bright coloration probably warns me off). The Western Tussock Moth instead have irritating hairs and other bright colors to warn potential handlers away.
Lesson: Always wear gloves if you touch an unfamiliar hairy caterpillar. Some can really irritate your skin, and you don’t want to deal with the itch.
Region also matter greatly, and so does geography within those regions. In the infographic above they map out where certain butterflies are found based off regional climate, coastal fog zones will have different species from the drier mountain ridge or foothill areas. For example, coastal spots tend to have Lorquin’s Admirals and pipevine swallowtails; the citrus-growing inland valleys tend to have giant creatures such as the Giant Swallowtail. (Getting to know what is in your region helps narrow down what to look for a lot.)
You don’t need to identify every worm that crosses your path. Instead, pay attention to the host plants in your landscape. Since things like ceanothus or oak species are natives, planting them can invite many species and transform your garden into a biodiversity hotspot. It is an investment worth making, and it offers big returns for the local critters.
Finally, know friend from foe. The chart shows where to look for unwelcome characters like cabbage looper and other pests that do harm. It also shows who is really fine company, as most caterpillars are. Handpicking works better than spraying broadspectrum pesticides, which also take out beneficial creatures besides the bad guys.
As you learn to observe well and garden mindfully, your protection helps keep up populations that has suffered drastic declines in just the past few decades. Every caterpillar plays a part, from the common monarch to the endangered Bay Checkerspot, and learning to recognize each one before it vanishes into a cocoon is the first step toward helping protect them, before all we’re left with is the great unknown: What will hatch next?