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  • Amanda


Updated: Sep 28, 2020

And now for something a little lighter...unless you're a gardener and then you'll be terrified. A new series "Voracious". It's about caterpillars, and how much they like to eat, as anyone who's read "The Very Hungry Caterpillar" already knows. But first, let's remember we shouldn't judge other life forms for how they get through life--birth, growth, maturity, making the next generation--aspirationally, we have a lot in common. And offspring that look like tiny decorated school buses are perfectly legitimate. Kudos to the butterflies and moths that invented this approach to childhood. But it gets personal when they decimate your grapevines, as these western grape leaf skeletonizers are wont to do. And to add insult to injury, they fight back with hydrogen cyanide whenever I try to deal with the problem. Ouch!

Part 2 in "Voracious". Cylindrical, and squiggly but clearly not worms, which can seem revolting. There's something different about the caterpillar shape we quickly spot, a little blunter at the tips, there's a distinctive head tucked into the front of the body, the thorax in 3 segments, each with a pair of hook-tipped legs, and behind that the abdomen helped along with its prolegs. All those subtle differences are encapsulated in the entomological term for the caterpillar shape: eruciform. Funny how little things like its shape, its cute prolegs and their clamping feet called crotchets make it endearing instead of gross. Maybe the humpy, up and down movement is intuitively less dangerous to us instead of the side to side squirm "Oh my god, it's a worm!!...oh, it's just a caterpillar." But objectively, that body shape is pure function. A closer look shows the caterpillar is about 90% stomach, and being eruciform is ideal for eating a lot, growing fast, and getting around. Because as it turns out, a caterpillar moves on stomach power, propelled forward by its intestines as it does "the wave"! Which has served this Sonoran tent caterpillar well, if that's what it is...I guess it's not too surprising there aren't many resources for caterpillar ID. If kids ran the world, there would be.

(thanks to Nick Dowdy for identifying this caterpillar as Gnophaela vermiculata, or police car moth, a bluebell-loving species, as the leaf in the picture shows.)

Part 3. Soft green skin, so soothing a color, and it bounces back to the touch! It makes you want to pet this little fawn sphinx. The furthest thing from the tough exoskeletons insects are known for. The skin, integument, cuticle--there are a few different words for it--is still an exoskeleton, but caterpillars, like all insects, have special powers that defy our ability to put things in boxes. The chitinous exoskeleton, which it turns out doesn't have to be hard--it can be as soft as a mushroom--is controlled by the caterpillar's single layer of skin cells underneath the chitin. In the places that need to be hard, the cells send up fixative chemicals. In the places that need to be pliable and stretchy, they leave things be. As you can imagine, the caterpillars need most of it pliable and stretchy to accommodate exponential expansion. And when the covering is stretched to its limit? It so happens the skin cells grow a new, softer version underneath and then the old covering splits and sloughs off, just in time for the next meal. Actually, it is their next meal. They molt about 5 times as they grow. It's functionally equivalent to us loosening our belts a couple of notches before 5 Holiday seasons.

Part 4. Being voracious starts with a mouth. This tomato hornworm caterpillar is shy about showing his, but if you look past the prolegs, their crotchets, the 6 tiny regular legs, and under the green goggle-looking fake eyes, below the tiny dots that are his real eyes.. you'll find his mouth. It's black, and wickedly serrated if you zoom in. These are his mandibles, built for biting and ripping, chopping and tearing. Somewhere in that jumble of indistinct body parts are segmented antennae for smelling, and maxillae for tasting and guiding the chopped leaf pieces into his mouth. Taste is key for caterpillars, because most of them are very particular about what they put into their mouths. Many of them eat only one or two different types of plant, so tightly intertwined with their plant species of choice they'd wither away without it. It's like a twisted love affair with the caterpillar intent on consuming his beloved, and his mouth the nexus where it all happens.

Part 5. Like little Chinese dragons, this band of milkweed tussock moths is decked out in the scariest, yet most decorative of outfits. Tasseled and plumed, they march around together, just showing off, it seems. How weird for such small and juicy tidbits, they're basically globs of fat there for the taking in a largely nutrient-poor environment. And that is the problem they've had to solve. A common caterpillar solution is to blend in and spread out. A different solution is to go on offense by banding together and looking intimidating. As with many other bright and hairy caterpillars, they've mastered plant alchemy, turning botanical chemicals into armaments laced with poison. Have you felt their stinging hairs? But like most creatures, they know an ounce of cheap advertising is worth a pound of high-cost offense, so looks matter!

Part 6. Just a fun topic, I thought. Cute, small, something I'd always been a little curious about. And easy enough to find six examples of. Of course, it went deeper than that, as with everything else in Nature. Caterpillars are all about potential. They take a plant and very efficiently go about turning it into caterpillar flesh. Their entire anatomy is optimized for doing this, from their head and its mandibles, down to their last pair of prolegs, and the immense stomach that lies between. It's a life of deciding whether it's the right leaf, eating the leaf, moving to a new leaf, expanding, storing up energy, protecting their gains, with the accompanying behind-the-scenes goings on at the cellular level. But it's actually just a life stage, so easily forgotten because their eruciform shape is radically different from what comes next: metamorphosis--a move this next caterpillar-a young white-lined sphinx moth--is about to make.

It might be exploring its options, but more likely is feeling the last dregs of juvenile hormone being replaced by its molting hormone, ecdysone. A strong urge to crawl down and find a nice out-of-the-way spot, where the skin cells will take over, this time to create a hard, protective covering. And then all hell will break loose. Inside the casing, all those caterpillar cells will be instructed to commit suicide and turn themselves into nutrient soup. The imaginal discs which have been lying dormant are primed to differentiate into moth parts. The hormones will unleash them, their cells proliferate and specialize, the soup will be converted to a fully functioning moth, and nothing will be left of the caterpillar.

It's a shocking and distasteful process to visualize--until you think about the orchestration at work. Not really mindless, needless voraciousness at all. There's a beauty in their single-minded focus on feeding, in the tight evolutionary dependency on a certain type of plant, and the amazing cellular coordination that underlies it all. Not cute, not gross, but an incredible facet of Nature that has been crafting a million smart design solutions all along, in the evolving symphony of life.

#yourlandexplained #naturalhistory #naturelessons #insects #caterpillars #entomology

#ecology #environmentaleducation #outdoorlearning #lepidoptera #moths

#sphinxmoth #colorado #milkweed

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