Monsters Mini-Post: On Caterpillar Defense Mechanisms, or, Sticking It to You

Some caterpillars possess amazing defense mechanisms, the kind that exist to make parents and guardians forever fretful when their kids go out to play. Other caterpillars mimic bird poop. I guess the phrase “different strokes for different folks” applies to the non-folks of the animal kingdom as well.

The photo that inspired today’s post.

Caterpillars are the larval forms of both moths and butterflies, squishy little worm-like creatures that emerge from eggs. Their squishiness makes them incredibly attractive to several members of the animal kingdom including birds and squirrels that, like me around midnight, are always on the lookout for a snack that’s easy to eat.

So to become a bit more difficult to eat, several species’ caterpillars have evolved features along their bodies that discourage other animals from poking at them, usually through the always discouraging use of toxic chemicals. The larval forms of such frequent flyers as the Io Moth, the Buck Moth, and the Hag Moth all have bodies lined with stinging hairs and quills that are connected to poison sacs. These hairs can break skin, allowing the toxic chemical to seep beneath them. Humans who get stung by these caterpillars may experience symptoms ranging from minor irritation to everybody’s favorite, intestinal discomfort.

Given how most people feel about having a churning sensation in their lower abdomens, it’s understandable that a lot of people avoid touching caterpillars just to be on the safe side. The majority of caterpillars are not stinging caterpillars, though. Unlike the stinging caterpillars listed above, others have bumps on their bodies that appear harmful but really are just for show.

One such caterpillar is the Black Swallowtail. During some of its larval stages (and larval stages are called instars, in case you were wondering, since science has names for everything), the Black Swallowtail’s body is lined with orange bumps that protrude from the surface. They look dangerous, because often in nature red and orange are used as colors that warn predators that they’re hunting something that will seriously screw them up, but Black Swallowtail caterpillars are considered by some people one of the best caterpillars for budding entomologists to try to raise.

So how do Black Swallowtail larvae stay safe? Well, they do have one protrusion that actually does mess with other animals. It’s called an osmeterium, and it’s a Y-shaped horn located at the back of the caterpillar’s head that pops out when the little squirmster is frightened and gets retracted when it once again feels safe. The osmeterium shoots a musty-smelling liquid that, while not harmful to humans, is tinged with a distinct whiff of eau du displeasure, enough to suggest that backing away is a good idea.

But before the osmeterium even comes into play, the Black Swallowtail caterpillar defends itself in another way: similar to the Tiger Swallowtail caterpillar, during its earlier instars, its body bears a splotchy white marking right in the middle. Does this white mark carry the same suggestion of poison that red body markings do? Nope. Does it make the caterpillar look like an unappetizing piece of bird poop that squirrels and other animals are likely to pass over without a second thought? It sure does!

No one ever said that survival can’t be crappy sometimes.

On Seed Dispersal, or, One Day I’ll Fly Away—Or Be Launched, Whichever

I use witch hazel extract on my face every night. It’s derived from the leaves and bark of the common witch hazel plant, Hamamelis virginiana, and in addition to cleaning the skin is supposed to help relieve it of irritation. In light of witch hazel’s calming properties, I guess it’s a little funny that a witch hazel plant starts out, very literally, with a bang.

For a plant to produce offspring and continue that beautiful circle of life that Elton John sang about, it has to send seeds out like children into the big, bad world, a process known as seed dispersal. And just as some parents and caretakers allow their children to keep living at home after graduation, maybe staying in the basement or the pool house, while others practically pack their kids’ boxes and suitcases for them, plants go about seed dispersal in any number of ways:

The photo that inspired this post.

• Letting gravity take its course

• Encasing their seeds in tasty fruits for animals to eat so that the seeds will later be, um, deposited (seed dispersal plus, now with a fertilizer bonus)

• Attaching lightweight structures that allow the seeds to drift serenely on the breeze

• Launching them violently into the surrounding environment

That last option probably sounds made-up. It isn’t. Witch hazel seeds develop inside of a capsule that bursts at maturity. Like a circus daredevil spewed from a cannon, each seed ends up shot about twenty to thirty feet away from the parent plant. The capsule makes a popping sound upon bursting—or a bang, to go back to where we started this.

It’s nothing like the method of seed dispersal that many trees here in the Midwest employ. Wind dispersal seems more appropriate for a plant that’s used to make a soothing extract. The way that whirlybirds or helicopter seeds like the ones seen in the photo above (the technical term for a winged seed like these is a samara, presumably because “whirlybird” never stuck in scientific circles) simply flutter to the ground perhaps offers a greater sense of enchantment than the botanical equivalent of cannon fire. Plus, as mentioned before, all the other plants are doing it: various trees including ashes, the winged elm (naturally), and most conspicuously maples all produce winged seeds.

So why doesn’t the witch hazel plant give in to peer pressure? Well, as helpful as winged seeds are in spreading a plant’s offspring far and wide, that huge range of dispersal (we’re talking hundreds of feet here) comes with certain trade-offs:

1. Not every seed is guaranteed to land somewhere hospitable and grow, so the parent plant spends a lot of energy producing seeds that will never germinate.

2. In order to be light enough to dance on the spring breeze, winged seeds aren’t packed with as much nourishment as, say, the seeds packed into fruits are. As a result, some will be too poorly nourished by the time they land to sprout.

3. Kids like to pick them up and toss them into the air, at least where I grew up, because it looks really neat (see trade-off #1).

No doubt that witch hazel’s exploding seed pod looks (and sounds) neat, too, but the exchange there is that it takes even more energy than making a load of winged seeds to actively expel a few seeds from one’s body. Each plant evolves the method of seed dispersal best suited to its environment. If it happens to delight us with showers of whirlygigs or sudden eruptions of seed pods, well, that’s just one more way we’ve benefited from evolution, I’d say. It’s right up there with opposable thumbs in scientists’ minds, I’m sure.

On White Clover, or, Wow, That Really Isn’t Lucky for Some Animals

Green is good! At least, that’s what we’re taught in our science classes when it comes to plants. Plants with healthy green leaves are busy getting down, doing photosynthesis (which, being a biochemical process, is actually the antithesis of getting down). They’re growing and becoming the mature leafy plant life that eventually animals like cows—or, you know, us—will eat for sustenance.

So why would a plant develop a pattern on its leaves that’s white? Why would a plant include code in its genes for a part of the leaf that doesn’t perform photosynthesis as well?

The photo that inspired this post.

White clover, known scientifically as Trifolium repens, exists throughout Europe, North America, and parts of the Pacific. A lot of people reading this blog have seen it, I bet. Chances are that a few of us as kids plucked it and shouted something like, “I found a lucky clover!” while holding a bunch of it in a small bouquet. Presenting our white clovers in a cluster, we reasoned, made it that much harder to tell that the plants we found growing everywhere really had three leaves instead of the fabled four. How clever we were! (Or, how clever I was, if I’m the only dork here who was sure that that would work.)

Okay, so we/I sucked at getting the adults around us to see what we wanted them to see. Trifolium repens, however, is actually very good at getting the creatures that eat it to notice exactly what’s important.

One widespread form of white clover (which has white flowers, if you were wondering) has leaves that are solidly green, just as you‘d expect from a plant. In contrast, another variety has a pale v-shaped stripe in the center of each leaflet.

That stripe doesn’t exist just for pretties. The variety of white clover with the v-stripe, sometimes known unsurprisingly as “white-striped clover,” produces cyanide inside its cells. It makes just enough of that lethal compound to cause problems for small creatures like snails and slugs that otherwise would eat whatever clover they could find in low-lying areas.

It should come as no shock that the striped white clover is the more common form of clover along low-altitude coastlines like that of Long Island, New York, of the shores of North Carolina, where plant-eating molluscs like to slither. Survival of the fittest, baby! The molluscs in such places have learned that that stripe means danger and so the striped clover lives on. If you want to see the plain form of white clover in abundance, Minnesota is cool. Not as many shell-toting animals in those plains thereas there are by the ocean.

Even if striped white clover is toxic to small animals (and even if any kind of white clover’s ability to grow quickly across a large area of land has led most people label it a weed), it is a green plant, and green is still good:

• Its flowers attract bees, those wonderful pollinators.
• It’s able to deliver the nitrogen that other plants need to grow into the soil, making it good for crop rotation (provided it doesn’t take over the land).
• It’s bovine approved—white clover often gets added to livestock feed to improve its quality.

In other words, one animal’s poison is another one’s lunch. I think that’s how the quote goes, anyway.

On Naked Buds That Are Actually Hairy Buds, or, Hey, Buddy

Military strategy and botany aren’t often considered in the same essay, but hey, sometimes it’s necessary to talk about defense.

The Greek phalanx is perhaps one of the best-known formations in military history, and not just because Gerard Butler drew attention to it with his astounding abs. The phalanx was a pain in the ass to penetrate: while Greek infantrymen—foot soldiers known as hoplites—stood in a tight cluster with their meter-long shields overlapping, they also stuck long spears through the gaps, daring anyone to come close and try to penetrate the dome of bronze and leather created by the shields. It wasn’t the easiest formation to maneuver through a battlefield, but it largely kept the hoplites safe.

The photo that inspired today’s post.

Plants, in contrast, generally don’t have to worry about moving anywhere, unless we’re talking about seed dispersal or Ents. They do, however, have to deal with insects and other herbivores gnawing on them, especially on their tender green buds (which sounds a little more pornographic than it really is, sorry).

Woody plants have two types of buds along their branches: leaf buds, which produce the small, leafy shoots that we also know as twigs, and flower buds, which pretty much let you know via their name what they produce. In either case, the bud is a site of fresh new growth for the plant, which means that the bud is important to protect.

Plants aren’t animals, though (and if this blog teaches you nothing else, let that be it). There is no ability for a plant to go all Mama Bear on invading insects and simply swipe them away, as impressive as that would be. Most woody plants instead protect their buds with bud scales, modified leaves that hide the new green growth. Like the shields, or hoplons, of the Greek foot soldiers, the scales often overlap. They also have a leathery texture; the hoplons, made partly from wood, had leather fastenings that allowed soldiers to secure the shields against the entire length of their arms.Granted, buds lack the bronze embellishments of hoplons, but you know, details.

But not every plant’s buds are covered by scales. Some plants, like sumac and the peach tree, as well as other herbaceous plants (which are plants with leaves and stems that die back to the ground every year), have buds covered with tiny hairs. Because they lack scales, these buds are considered naked buds, which means that, yes, like your last date, plant buds can be both naked and hairy. Hey, buddy, indeed.

The hairs serve a similar purpose as the spears of the phalanx did: they keep attackers away. Specifically, they do an excellent job of preventing critters like caterpillars from munching on the bud tissue, which the hoplites never had to contend with, but the principle is close enough. In this way, the world’s flora demonstrates how adept it evolved to be at fending off onslaughts.

Nature: it’s a battleground. And war can get hairy.

On Water Sprouts, Tentacles, and Growth, or, Hail Hydra!

Ask just about any person who’s gone through puberty: hormonal changes can have some interesting effects on human growth.

They can have some interesting effects on plant growth, too. Like humans, plants have hormones running through their systems. True, plant hormones aren’t the same as the ones found in humans and other animals, and they act in completely different ways than animal hormones do. When it comes to trees, though, in some cases plant hormones have an effect similar to the one that testosterone and everything else in the human chemical cocktail had on most of the boys in my junior high class: they cause them to grow long, spindly limbs.

Like other plants, trees produce hormones in different parts of their bodies, such as the tips of their branches and deep down in their roots. When those parts get damaged, the distribution of hormones throughout the tree changes. Suddenly, the redistributed hormones cause thin, quick-growing branches to develop from previously dormant buds, called epicormic buds, along the branches and trunk.

The photo that inspired today’s post.

The shoots that arise from these slumbering buds are known commonly as water sprouts. When water sprouts grow along other branches, they grow vertically, shooting straight up toward the sky like hands of the newly risen dead bursting forth from the grave in a zombie flick. When these monsters shoots emerge from the trunk, the concept of vertical growth sometimes gets a little tentacle-y instead, as you can see in the photo that inspired this post’s illustration.

Aside from their occasional resemblance to Lovecraftian appendages, water sprouts are discouraged for other reasons. As some  have pointed out, water sprouts block air and light from moving among a tree’s branches, inhibit fruit growth, break easily, and divert energy from stronger branches.

Water sprouts also grow back easily, as pruning a water sprout creates a fresh wound that the tree ends up attempting to compensate for with new limbs and more leaves for carrying out photosynthesis. It’s not quite the same as the whole cut off a limb, two more will take its place dynamic that fans of Marvel Comics will appreciate, but it does make plant growth one more example of regeneration in nature, alongside some impressive mentions from the animal kingdom:

• Of course, the hydra, a relative of jellyfish, with tentacles that would make a tree with water sprouts feel envy if trees could feel such emotion. The hydra constantly generates new cells, meaning that if a hydra is cut in half, the cells from the creature’s main body column will differentiate. One half will grow a new head; the other will grow a new foot. And the cells retain a “memory” of which side of the body is up and which is down, even after being spun in a blender, which is better than I can do after a roller coaster ride.

• Octopuses, while I have water sprouts and tentacles on my mind (though an octopus’s appendages are referred to as arms, not tentacles). Male octopuses use one of their eight arms, called a hectocotylus, specifically to give packets of sperm to their female mates. It’s a gift that keeps on giving: males of such species as Abdopus aculeatus lose that arm during copulation and regrow a new one later.

• Salamanders, such as the axolotl. Thanks to the activity of certain genes, along with a little bit of electrical stimulation that’s believed to be carried along nerves, salamanders can regenerate a lot of their organs, including parts of their brains and spinal cords.

• Can’t forget about flatworms, a.k.a. planaria. As researcher Thomas Hunt Morgan discovered in the 1890s, cut one flatworm up into 279 pieces, and 279 more will come back to take its place. It’s fascinating any time the action of genes ultimately triumphs over the action of a knife.

Human beings exhibit a lot of different kinds of talent that other forms of life on this planet don’t. You’ll never hear about an octopus preparing dessert or a tree repairing a car’s transmission. When it comes to composing operas, I feel pretty confident in declaring that no other organism here has us beat.

When it comes to regenerating parts of our bodies that get damaged, however, compared to other creatures, we might seem rather unimpressive. Some parts of our bodies can regrow over time; the liver is a notable example. But brains, or even our fingers? We’re notably capable when it comes to reworking the world around us, notably less capable when it comes to repairing ourselves.

At least, we are right now.

Some researchers believe that the genes like the ones that stimulate regeneration in flatworms and salamanders could be activated in human beings, too. If so, human development could go well beyond the awkward growth spurts we experience around age 13. We could begin treating severe injuries in ways previously unimaginable.

Hail Hydra indeed.