They’re fire-engine red, a color cue to say: Stop! Don’t touch me! A million-plus years of evolution produced that message in those brash-bodied caterpillars. Nature’s alarm bells rarely ring casualy; red says: I’m here. And 12 common creatures feature that flashy hue in their life-defining schemes (above), says the infographic. But the graphic’s just half of the story.
Why did nature pick red instead of brown or green? That’s what this tells us about why these larvae thrives. To stay out of view as food, most caterpillars blends in with leaves and stems. Instead, red ones scream, “I’m here!” from branches. That’s called aposematism, or honest advertising. The animal is telling every bird and frog nearby that it taste terrible or stings badly.
Why Caterpillars Are Red
One example is the Cinnabar Moth larva, which is brightly banded in red and black and feeds on Ragwort plants. But it doesn’t just eat them, it take in toxins in plant tissues itself. After a single nasty meal, a predator quickly remembers never to mess with anything striped again. This provides better protection for species than staying camouflaged could of.
But not all red caterpillars threaten. Some are simply dressed up as the real deal. That’s what’s called Batesian mimicry. Harmless animals develops patterns like their dangerous cousins because imitation comes free, but avoiding being eaten does not. For example, the early instar of the Spicebush Swallowtail imitates something it isn’t (dangerous); but doesn’t need to be: It’s just a bit of bird droppings with fake eyespots. To a predator, it’s enough since no one has time to fact check every creature out in nature. Get up close to its host plant and you’ll see who’s who.
Your first clue when identifying a caterpillar: That chart lays out specific hosts for each species to help with identification. If you see a red larva on milkweed, for instance, be cautious as those loose hairs may cause irritation. Alkaloids can mean toxic trouble, especially with ragwort. Do not fear the scary-looking head hump on the Red-humped Caterpillar shown above. Even though he feed on oak trees, he is perfectly harmless. He is also harmless to his tree host.
You can’t identify the creature without knowing what it eats, but then context is everything: in the garden, where does it find its chemical weapons or a place to call home? And then there are spines, which seem insignificant until one realizes their variety. Some look scary but is soft to the touch, such as on the pipevine swallowtail prior to pupation. Other hair-like setae (setae) may comes off and give you a rash. Certain hollow spines even has poison inside them and can inject it into you.
Here’s where looking at something closely from afar helps: If you get up close to take a photo of it, you can zoom in later and study the critter in detail without fear of a rash or sting. Curiosity kills fewer cats than carelessness do when it comes to what’s in your own yard.
That still leaves dozens of potential culprits. However, it also narrows things down seasonally. Most of them has their largest populations in summer. This is the time of year their larvae grows fastest and there is plenty of food (leaves) for them to gobble up. If you find one in October, it might be a late hatch, or it might belong to an overwintering species.
Some are native only to certain parts of North America; others are imports from Europe, which helps narrow down what you might encounter. That’s why knowing your area’s geography can eliminate more potential culprits than anything else, meaning you seldom need to fret about all those species above unless you live within their range.
Insects gets the message that red means respect, whether that message is true or false. This makes the message real as an evolutionary force. The color lessons become a bio-lesson in walking through the garden, where what was once a hazardous area becomes one of understanding. Suddenly you can see the struggle between prey and predator unfold on each stem. You learn to read the colors next time you pass something with a flash of red on a leaf, stopping your hand instead of reaching forward. After all, nature has made sure you will want to stop and take another look at the very least.